We ............. when we decided to stop and rest. a) were driving b) had been driving c) have been driving d) have driven

To determine the correct option for the sentence "We ............. when we decided to stop and rest," we need to analyze each choice in the context of past actions.

1. Option a: were driving
   This suggests a past continuous action. It implies that the driving was ongoing when the decision to stop occurred. This option fits well in the given sentence.

2. Option b: had been driving
   This indicates a past perfect continuous action, suggesting that the driving had been happening before the decision to stop. While it could work, it is not necessarily the most straightforward choice for this specific sentence.

3. Option c: have been driving
   This is the present perfect continuous tense, indicating that the action of driving started in the past and is still continuing to the present. This does not fit well with the context of having made a decision to stop.

4. Option d: have driven
   This is the present perfect tense and implies completion of an action, which does not align with the decision to stop and rest being part of an ongoing action.

Conclusion

The best fit for the sentence is a) were driving, as it indicates that the action of driving was in progress when the decision to stop was made.

Final Answer: a) were driving