**Rule:** The Future Perfect Tense (will have + past participle) is used to express an action that will be completed by a specific point in the future. 'By the time the documentary is over' sets the future deadline by which the action of learning will be complete. Option (c) suggests the learning will be in progress, not finished.

**Rule:** The Future Perfect Tense (will have + past participle) is used to express that a future action will be completed before another future event. The action of finishing the presentation will be done by the time the boss calls. Option (b) implies the action will be in progress at that moment.

**Rule:** The Future Continuous Tense (will be + verb-ing) is used to describe an action that will be in progress at a specific time in the future. 'This time next month' pinpoints the future moment when the action of flying will be happening. Option (d) suggests the flight will be over by that time.

**Rule:** The Future Perfect Passive (will have been + past participle) is required. The action ('open') will be performed on the subject ('bridge'). The action will be completed by a specific future time ('This time next month'). Option (b) is future continuous active. Option (c) is simple present active. Option (d) is simple present passive.

**Rule:** This is a First Conditional sentence (if + simple present, ... will + base verb), used for real or likely future situations. The main clause expresses the future result of the condition. 'will not speak' correctly states the future consequence. Option (b) 'is not speaking' is Present Continuous. Option (c) 'doesn't speak' is Simple Present and grammatically incorrect in the main clause. Option (d) 'would not speak' is used in the Second Conditional for hypothetical situations.

**Rule:** The Simple Present Tense is used to talk about future events that are part of a fixed schedule or timetable (like public transport, meetings, or classes). Since the train's departure is a scheduled event, 'departs' is the correct form. While options (a), (b), and (d) can all refer to the future, the simple present is the most natural and common choice for timetabled events.

**Rule:** The Present Continuous Tense ('is/are' + verb-ing) is used to talk about confirmed plans and definite arrangements for the future. The phrase 'It's confirmed' clearly indicates a fixed plan. Option (a) is for predictions or spontaneous decisions. Option (b) is for schedules. Option (d) is future perfect.

**Rule:** This question tests logical deduction about a past event with present evidence. The modal verb of deduction 'must have' + past participle is used to express a strong conclusion about the past. The present evidence is 'the lights are off'. The conclusion is that they have already left for their holiday. The other options refer to the future, which doesn't fit the evidence.

**Rule:** The Future Perfect Tense (will have + past participle) is used to express that an action will be completed by a specific future time. The action of 'speaking to at least twenty people' will be finished by the end of the meeting. Option (a) suggests the speaking will be in progress, not completed.

**Rule:** The Future Perfect Tense (will have + past participle) is used to express the completion of an action by a specific future time. 'This time next year' is the future deadline by which the action of paying off debts will be complete. Option (b) is a simple prediction but doesn't emphasize completion as strongly.