Answer :
She is on a diet. She ate nothing but bananas for the last month
She is on a diet. She has been eating nothing but bananas for the last month.
The correct answer is B. The question above is about selecting the right verb tense. In this case, it is the Present Perfect Progressive tense.
When to use Present Perfect Progressive tense.
They are used mainly to explain ongoing events. How can you tell that the event is still ongoing? see the first part of the sentence. It states that She is on a diet.
See the link below for more about Present Perfect Progressive tense.
https://brainly.com/question/540517