puzzling

[*^^*]

The country has already sent up three unmanned spacecraft, the most recent _______ at the end of last March.
A. has been launched B. having been launched C. being launched

some teachers say that the comma can not connect two sentences, so A is incorrect,
and there is an exact time "at the end of last march" , not "since last March" so B is incorrect, too?

but other teacher think B is correct, because they think this event has already finished.

[Verona_82]

Not a teacher. I chose alternative C first, but then thought a bit and changed my mind. I think B is correct. That's Perfect participle that acts as an adverbial modifier. It has nothing to do with "present perfect +since".

[bhaisahab]

Both B and C are possible.

[5jj]

The country has already sent up three unmanned spacecraft, the most recent _______ at the end of last March.
A. has been launched B. having been launched C. being launched

some teachers say that the comma can not connect two sentences, so A is incorrect, It's not so much the comma as 'at the end of last March' that makes the present perfect inappropriate.
and there is an exact time "at the end of last march" , not "since last March" so B is incorrect, too? No. The 'perfect participle' is used as an equivalent of both present and past perfect and also of past simple contructions.

Having been invited six times, I think I'd better accept this time.
Having been invited six times, I thought I'd better accept his last invitation.

.

This is the sort of multiple choice question I detest. I think the writer expects the anwer B, but both B and C are possible for most speakers.

[Raymott]

some teachers say that the comma can not connect two sentences, so A is incorrect, It's not so much the comma as 'at the end of last March' that makes the present perfect inappropriate.

But the comma would also make it wrong, as the original poster said. For example, this is wrong:
"The country has already sent up three unmanned spacecraft, the most recent was at the end of last March."
You need a semicolon here.