when I need to omit the rest part of infinitive,but keeping "to"

Question

A: Are you going to watch the football match this afternoon?

B1: I'd like to, but B2: I'd like, but B3: I'd like to watch, but

which answer is correct? Is there any Grammar here?

Answer 1

This can be answered by consulting a dictionary for to:

often used by itself in place of an infinitive verb when the verb is understood

You can go if you want to. [=you can go if you want to go]

“You left the door unlocked.” “I didn't mean to.”

In the second example, "I didn't mean to" could be replaced by "I didn't mean to leave it unlocked."

Let's look at your example:

A: Are you going to watch the football match this afternoon?

B1: I'd like to, but B2: I'd like, but B3: I'd like to watch

B1 and B3 sound fine.

"Are you going to watch the football match this afternoon?"

"I'd like to, but ..."

This will be understood to mean "I'd like to watch the football match this afternoon, but ..."

"Are you going to watch the football match this afternoon?"

"I'd like to watch, but ..."

This will be understood the same way.

The problem with B2 is that it sounds incomplete.

"I'd like..."

The listener will be wondering "You'd like what?"

Is there any Grammar here?

Grammatically this is probably known as ellipsis, or omitting certain parts of a sentence when they are understood. Usually you try to omit enough of the sentence not to sound repetitive, but not too much for the statement to sound incomplete. To the question above, you could have answered without ellipsis in this way:

"Would you like to watch the football match this afternoon?"

"Although I'd like to watch the football match this afternoon, I have an appointment this afternoon."

However, this response is very wordy. Often we tend to want to omit repetitive parts of sentences. The most obvious way is by substituting a pronoun. Another way is to simply omit a clause. For example:

"Although I'd like to, I have an appintment this afternoon."

You can think of the part following "to" as having been omitted. Or you could omit "this afternoon" in both places like this:

"Although I'd like to, I have an appointment."

In both cases, your listener will probably understand that your appointment is in the afternoon, and that what you would normally like to do is to be watch the football match this afternoon.