Question

1. 4. Select the prepositional phrase(s):
Look under the desk for your books.
A. under the desk for your books
B. look under
C. the desk for
5. Select the prepositional phrase(s):
I like to learn about Asian Americans
A. I like
B. about Asian Americans
C. to learn

Answer 1

For the first one, it's (A) because you're asking the question "WHERE am I supposed to look?" - Under the Desk... but I think that for your books should have been removed, and the question isn't "What are you looking for?". It's also not telling you "What am I doing?" That answer would have been B.

for the second question, it's the same. "I like to learn about Asian Americans"
What do you like to learn about?
About Asian Americans.
Therefore, (B) is the answer.