Which sentence is an example of the future simple tense?

The correct answer is A. I shall eat.

Explanation: The future simple tense is used to describe actions that will happen in the future. In this case, “I shall eat” indicates that the action of eating will take place at a later time. The other sentences represent different tenses: “I was eating” is past continuous, “I am eating” is present continuous, and “I had eaten” is past perfect.