Which word completes the sentence correctly: He wanted to go out, but he __________ to finish his homework first?

The word "had" is the correct choice to complete the sentence because it effectively indicates a past tendency or obligation. The sentence implies that there was a desire to go out, but an obligation or necessity to finish homework first existed in the past. Using "had" captures this past context and suggests that he ultimately prioritized completing his homework over going out.

In contrast, "was" would imply a state of being, which does not convey the same sense of obligation or intention of completing the homework first. "Is" reflects the present tense, which does not fit the retrospective context of wanting to go out but needing to finish homework first. "Could" suggests an ability or possibility, which does not match the intent of expressing a prior obligation that had to be addressed before taking another action. Hence, "had" is the most suitable choice as it maintains the correct past tense and meaning needed in this scenario.