The second and last highlighted parts
The study of behavior and why people do the things that they do.
Answer:
While I <u>was taking</u> a shower, my cell phone rang. I asked my sister to answer it, but she didn’t hear me because she <u>was cleaning</u> the backyard.
(it's the first option)
You cannot put any sort of endmark (period, question mark, or exclamation point) here because it is not a complete sentence. Complete sentences must have a subject and a predicate. You can tell there's not even a verb here, so this is just a fragment, and we would have to use a comma.
a. Very truly yours,
