I am now doing the grammar excises by the English Grammar in Use.
I have some questions below about present perfect and past simple.

1. Drugs have become a big problem everywhere.
Can I change "have become" to "become"? Use present
-tense simple.

I studied German at school, but I have forgotten most of it now.
The second sentence could use past-tense simple? --
> .... I forgot most of it now.

3. A
:Have you heard about Ben? He has broken his arm.
B: Really? How did that happen?
second sentence of Acould use past-tense simple too?--> ... He broke his arm.