present simple vs perfect

[ibra121]

Hi everyone, I want to which sentences is correct and what are the differences in meaning ?

A: Self-help groups have become very common all over America.

B: self-help groups become very common all over America.

[engee30]

Hi everyone, I want to which sentences is correct and what are the differences in meaning ?

A: Self-help groups have become very common all over America.

B: self-help groups become very common all over America.

♥♦♣♠ NOT A TEACHER ♥♦♣♠

As for sentence A - you might look at it as if you were trying to put emphasis on the fact that self-help groups were very common all over America in the recent past, are still and may be so in the future. You treat the present moment as the point of reference - you refer to a situation having its start in the past leading up to the present moment.
Sentence B simply tells us about the fact of self-help groups becoming very common all over America. It's a matter of emphasis, to my mind.

[5jj]

B: self-help groups become very common all over America.

If you want to talk about a situation that one can observe now, then B is unlikely. Far more natural would be:

Self-help groups are becoming very common all over America.

B is likely only when we are talking about a general case:

Self-help groups become very common all over America in times of economic stagnation.

[allenman]

Hi everyone, I want to which sentences is correct and what are the differences in meaning ?

A: Self-help groups have become very common all over America.

B: self-help groups become very common all over America.

As an AmE native, A sounds perfectly ok. B can not stand on its own.
The suggestion by fivejedjon simply indicates a continuing state (present progressive) where sentence A states a general fact. No need IMHO to add the progressive here.

Not a teacher

[5jj]

As an AmE native, A sounds perfectly ok. B can not stand on its own.
The suggestion by fivejedjon simply indicates a continuing state (present progressive) where sentence A states a general fact. No need IMHO to add the progressive here.

I think A sounds fine, too.

I was writing only about B. I implied what you made explicit 'B cannot stand on its own. My two suggestions were either to use a progressive form or to add something to the original B.