In the quest of finding out the fine distinctions between the present perfect and the simple past, I'd like to pose the following questions. Any help will be appreciated

1- I ---- your wife in the shopping mall.

A) saw B) have seen

2- Who ---- you?

A) has called B) called

3- She ---- up with an interesting idea!

A) came B) has come

4- I ---- that.

A) haven't known B) didn't know

5- Well, many ESL learners find it difficult to choose which tense to use, simple past or present perfect. Apart from the general guidelines supplied in the coursebooks or grammars, how do you decide which tense to use? the past - present relation requiring the present perfect does not seem to be covering all of its usages. I did my math homework. I have done my math homework. In both cases, my homework is ready to inspection by the teacher, isn't it? Why do you use one rather than the other? or "I would never treat my relatives in the way that Jim has treated his relatives." Why not "treated"? As you see, I wonder the real trick. or am I making it sound more difficult than it really is!
Thank you, Marius. The link is to the point.