Which of the following sentences is punctuated correctly?
a. do you think the hummingbirds will come back!
b. hummingbirds are kind of interesting!
c. when i see a hummingbird, i get so excited?
d. i love hummingbirds!

I will dissect each sentence for you.

A. Do you think the hummingbirds will come back!
No, this isn't it. It's a question, so it needs to end in a ?.

B. Hummingbirds are kind of interesting!
This might be it, considering the fact that this a direct sentence, but the exclamation point isn't needed.

C. When I see a hummingbird, I get so excited?
No, this isn't a question.

D. I love hummingbirds!
Maybe, since this is more of stating a fact and getting excited about the hummingbird which is nonetheless an animal/object.

Left choices:
B and D.

I'd have to say...

D, since B is kind of just stating something is interesting rather than loving something, however, both are punctuated correctly.

D