Last month tomatoes were quite cheap.

The correct answer is A. inexpensive.

Inexpensive means not costing much money. Costly means having a high price. Insufficient means not enough. Less means smaller in amount or degree.

In the sentence “Last month tomatoes were quite cheap,” the word “cheap” is an adjective that describes the price of tomatoes. The sentence is saying that tomatoes were not expensive last month. Therefore, the correct answer is A. inexpensive.