Which punctuation mark belongs at the end of the sentence?

what a wonderful gift

a.
.

b.
!

c.
?

What did cherry mean when she said, “things are rough all over” ? the outsiders

The tankers are so large how did some crew members get from one point to another while on board

How can you avoid the problem of groupthink? a. by choosing a group leader to direct the group b. by composing the team of only like-minded individuals c. by encouraging all members to voice their opinions d. by keeping quiet when you disagree with another group member's opinion