when to add the plural form "s" on a sentence?

hi everyone! some questions:

1) The result of some medical exam were spurious.

- should it be the results? or results? is "the result" here considered as plural already

- should it "be medical exams" if it meant a number of exams? how does "some" affect the word "medical exam"?

2) Everything is falling into place.

- why not "places"?

3) I have a lot of concern.

- why not concerns? since it meant a lot why not use the plural form of "concern"?

4) He had plenty of choice.

- should it be "choices"?

thnx everyone!