Correct Answer:
D. From
The correct answer is From. The verb "refrain" means to stop yourself from doing something, and it is always followed by the preposition "from". The correct structure is "refrain from doing something". Among the options:
- With: Incorrect; we do not say "refrain with".
- Of: Incorrect; "refrain of" is not standard.
- By: Incorrect; "refrain by" is not used.
- From: Correct; the phrase is "refrain from doing".
Thus, the correct preposition is "From".