The Future Continuous tense ('will be' + V-ing) is used to describe an action that will be in progress at a specific time in the future.

The Present Perfect Continuous tense ('has been' + V-ing) is used for an action that started in the past and continues to the present, especially with 'for' indicating a duration.

The action of missing the flight happened before the action of not being able to attend the meeting. Therefore, the first action must be in the Past Perfect tense ('had missed').

The preposition 'for' is used to denote a period of time ('three years'), whereas 'since' is used to denote a point in time (e.g., 'since 2021'). The correct phrase is 'for three years'.

The movie starting is the first past action, which must be in Past Perfect tense. Reaching the cinema is the second past action, which is in Past Indefinite.

Future Continuous ('will be' + V-ing) is used to indicate an ongoing action at a specific point in the future.

'Since' is used with a specific point in time (the morning). 'For' is used with a duration of time (e.g., for two hours).

The first completed action (finishing homework) uses the Past Perfect tense ('had finished'). The second action (going out to play) uses the Past Indefinite tense ('went').

Option B correctly uses Past Indefinite ('I saw') for the second action and Past Perfect ('had left') for the first action. Option A is wrong ('for a long time'). Option C is wrong (tense mismatch). Option D is wrong (tense order is reversed).

The sentence is grammatically correct. The action that happened first ('The meeting had begun') is correctly in the Past Perfect tense, and the action that happened later ('we reached') is correctly in the Past Indefinite tense.

The Future Continuous tense ('will be + verb-ing') is used to express an action that will be in progress at a specific time in the future. 'Will be starting' indicates the action will be happening at 9 PM.

The Present Perfect Continuous tense ('has been working') is used for an action that started in the past ('since 2005') and is still continuing in the present.

When two actions occur in the past, the one that happened earlier is put in the Past Perfect tense ('had died'), and the one that happened later is in the Past Indefinite tense ('reached').

The preposition 'since' is used for a specific point in time (e.g., Monday, 9 AM, 1990). 'For' is used for a duration or period (e.g., three days, two years). The correct phrase would be 'since last Monday'.

The Future Continuous tense ('will be decorating') is used to describe an action that will be in progress at a specific time in the future ('This time next month').

The Past Perfect Continuous tense is used here to describe a past action ('working all day') that continued up until another past action ('got home') and explained its result ('was very tired').

The preposition 'for' is used to denote a period of time or duration. 'More than an hour' is a duration, so 'for' is the correct choice.

The guests leaving happened before she arrived. Therefore, the earlier action takes the Past Perfect ('had already left'), and the later action takes the Past Indefinite ('arrived').

The phrase 'two days' is a duration of time, not a specific point in time. Therefore, it requires the preposition 'for', not 'since'. The correct sentence is 'She has been feeling unwell for two days.'

The sentence is grammatically correct. The Past Perfect ('had finished') is correctly used for the action that occurred first, and the Past Indefinite ('asked') is used for the subsequent action.

The Future Continuous tense ('will be presenting') is used to describe an action that will be in progress at a specific point in the future ('At this time tomorrow').

The preposition 'for' is used for a duration of time. '9 o'clock' is a specific point in time, which requires the preposition 'since'. The correct phrase is 'since 9 o'clock'.

The Present Perfect Continuous tense ('has been learning') is used to describe an action that started in the past, continued for a period ('for three years'), and is still relevant to the present.

The action of leaving the wallet happened before the action of reaching the restaurant. Therefore, the earlier action must be in the Past Perfect tense ('had left') and the later action in the Past Indefinite tense ('reached').

The Future Continuous tense ('will be sleeping') is used to indicate an action that will be in progress over a period of time in the future, which is implied by 'after 10 PM'.

'The last decade' represents a duration or period of time (ten years). The preposition 'for' is used to denote a period of time with perfect continuous tenses.

The action of seeing the film happened before the action of not wanting to see it. Therefore, the earlier action should be in the Past Perfect tense. The correct verb form is 'had already seen'.

The question 'How long...' asks about the duration of an action that started in the past and continues into the present. This requires the Present Perfect Continuous tense ('have been researching').

Sentence C correctly uses Past Indefinite ('arrived') for the later action and Past Perfect ('had already left') for the earlier one. A is wrong ('for many years'). B is wrong ('will be finishing'). D is wrong ('has known').