Emotion: crying I'd like to know which tense to use in the following examples:

1. "Oh, I ..... beautiful lamps there!"
a- 've often seen
b- often saw

2. You surely ... who... the championship last year?
a- didn't forget ... won
b- didn't forget ... has won
c- haven't forgotten ... has won
d- haven't forgotten ... won

3. "Did you buy the paper?" "I did, but I ... to buy some bread."
a- forgot
b- have forgotten
c- either a or b

4. After you ... he decided to accept.
a- had phoned him
b- have phoned him

5. 20 people ... killed during last week's riots.
a- were
b- have been
c- either a or b

6. She ... an ankle; I believe she ... while playing tennis.
a- 's spained ... fell
b- 's sprained ... 's fallen
c- sprained ... 's fallen
d- 'd sprained ... fell

7. He taught at St Michael's College ... 34 years.
a- while
b- during
c- for
d- any of these answers

8. Many people lost their jobs ... the last year of his Presidency.
a- during
b- while

9. Tremendous changes have occurred ... the past few years.
a- Ø
b- over

10. It ... years since I ... of the price of petrol going down.
a- is ... had heard
b- was ... had last heard
c- was ... last heard
(- has been ... hear)

And I would also like to know if both
"It's two months since they divorced" and
"It's two months since they have divorced"
are correct.

Thank you very much in advance!
Probably 1 should be a, but you could use b if the context is referring to somewhere, where you quite obviously no longer go.

6a or 6d (there is a typing error in 6a!)
7c (none of the others can be used)
9b - it would have been correct to use during here, but obviously the exercise didn't give you that option.

In my opinion only "It's two months since they divorced" is correct.
Thank you very much Elisabeth! Your comments help me a lot!