In which one of these sentences is a prefix used in an italicized word?
a. she was solely to blame for the quarrel.
b. she was ungrateful for his .
c. she pleaded with him not to leave.
d. he left when she shouted at him.

The answer is B. She was ungrateful for his help.

Explanation:

Among the four options offered in the question, only one presents a prefix. It is option B. She was ungrateful for his help.

A prefix can be defined as a letter or group of letters added to the beginning of word with the intention of altering its meaning by forming a different word. In the sentence in letter B, the adjective grateful, which means thankful, has been changed by the prefix un-, which means "not". Thus, ungrateful expresses the very opposite meaning of grateful. If she was ungrateful for his help, she did not feel or show any sort of appreciation for it, she was not thankful.