I. be going to do...

1. expresses an action that is going to happen after prior consideration and intention, according to plan or arrangement. For example:

(1) I ' m going to finish the report this afternoon. 2. expresses the action that is going to happen according to some kind of indication. For example:

(1) Look at the dark clouds in the sky. It ' s going to rain.

Second, will/shall do...

It means that there is no subjective will on the part of the subject, that it is a simple action that is going to take place, or that it is not considered beforehand, but that it is just a decision at the time of speaking to do something. For example:

(1) I shall write him a letter tomorrow.

Three, be doing...

Suggests that the most recent action will take place according to a plan or arrangement, which is limited to a few verbs, such as play, have, sleep, wear, etc., or verbs (phrases) that indicate displacement, such as go, come, leave, start, begin, move, drive, fly (take a ride on a plane), or to move, drive, fly (take a ride on a plane). move, drive, fly (乘飞机)

（1）We are having an English evening tonight.

4. The General Present Tense of Verbs

1. The general present tense is used to express future time, usually emphasizing an action that is expected to take place according to a rule or schedule, and is often used in conjunction with a future time phrase. The verbs used in this structure are go, come, leave, begin, start, sail, arrive, meet, return and so on. For example:

(1) My plane leaves at seven. My plane leaves at seven.

2. In the conditional clauses guided by if, unless, even if, and in the verbs guided by when, before, after, until, till, as soon as, by the time, each time, the moment, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time, the time. the time, each time, the moment, immediately, etc., the general present tense is often used to express the future time. For example:

(1) Unless you try, you will never succeed.

V. be to do...

It means to do something according to a plan, to arrange an upcoming action or to plan to do something. For example:

(1) The new Prime Minister is to speak on TV tonight.