Answer:
1. from
2. on
3. in
4. of
5. about
Explanation:
A preposition can be defined as a word that shows or illustrates the relationship between a pronoun or noun and other words in a sentence. Some examples of a preposition used in various literary works in English language are up, below, after, by, against, for, over, at, to, etc.
Hence, filling the missing words into the sentences we have;
1. She was hoping to borrow a book from her brother.
2. He is struggling to concentrate on his to-do list.
3. Are you interested in learning to dance.
4. They think that I am afraid of the dark.
5. We are excited about finishing the quarter.
In conclusion, the main purpose of a preposition in English language is to introduce an object by using (of, upon), indicate a timeframe by using (from, by, over), show direction by using (to, across, along), location or place by using (at, up, after, below) and to illustrate the spatial or sequential relationship between two or more things, people, place, etc.