What is the most effective combination of these sentences?

I had the following question on a practice exam:

4. Sentences 4 and 5: Now we're looking for at least ten volunteers. The volunteers will wrap the presents.

The most effective combination of sentences 4 and 5 would include which group of words?

(a) to wrap the presents
(b) who can wrap the presents
(c) In order to wrap the presents
(d) Now we need to wrap the presents
(e) for the wrapping of the presents

What do you think the correct answer would be and why?

My logic went as follows: (e) sounds much too contrived, and (d) means you have to rearrange the sentences too much and you have to add to it, i.e. "Now we need to wrap the presents and are looking for at least ten volunteers." However, (a), (b), and (c) all sounded viable to me. Option (a) would read "Now we're looking for at least ten volunteers to wrap the presents." Option (b) would read "Now we're looking for at least ten volunteers who can wrap the presents." Option (c) would read, "In order to wrap the presents, we're looking for at least ten volunteers."

According to the answer sheet in the back of the book, the correct answer is option (a) because "it smoothly combines the ideas in the two sentences. Options (b), (c), (d), and (e) do not combine the sentences smoothly." And that's all the further explanation it gives! It seems to me they are just being nit-picky.

Why do the other options not combine the sentences smoothly? Can anyone explain it?