3. He (play) computer games when his mother came in. a) were playing b) was playing c) played

The correct answer is **b) was playing**. **Explanation:** This sentence describes an action that was in progress when another action interrupted it. The action "playing" was happening when the action “came in” happened. Therefore, we need to use the past continuous tense for the verb "play," which is "was playing." Option C is simple past, which indicates a completed action, not an interrupted one. Option A uses “were”, which does not match singular “He”.