The film ____by the time we get to the cinema.

1. Future perfect tense: The future perfect tense is used to describe an action that will be completed before a specific point in the future.

2. Rule for future perfect tense: It is formed using the future tense of the auxiliary verb "will" or "shall," the word "have," and the past participle of the main verb.

3. Correct sentence analysis:

- "The film" is the subject of the sentence.

- "will already have started" is the future perfect verb phrase.

- "will" is the future tense auxiliary verb.

- "already" indicates that the action will be completed before a certain time.

- "have" is the auxiliary verb indicating completion.

- "started" is the past participle of the main verb "start."

4. Incorrect options:

- "will already start": This option lacks the completion aspect provided by the future perfect tense.

- "will already be started": While grammatically correct, it doesn't express the perfect aspect of completion that "will already have started" does.

So, the rule involves using the future perfect tense to express actions that will be completed before a specified point in the future.