Sentence Correction

Hey guys,

Considering parallelism of comparatives, which of the following sentences are preferred?

A)
1) John is bigger than Joe
2) John is bigger than Joe is (my guess)

B)
1) This year's GDP is higher than last year
2) This year's GDP is higher than last year's
3) This year's GDP is higher than last year was
4) This year's GDP is higher than last year's was (my guess)

C)
1) Like John, Linda likes flowers
2) Like John does, Linda likes flowes (my guess)

What are the general rules for "full" comparatives, i.e., those that add a verb to complete parallelism?

Thanks for your help!