い - Adjectives cannot be used with だ
Q: Why is the answer provided at the end of the review question?
A: Bunpro is a grammar-learning resource and not vocabulary focused. Therefore, we only expect you to determine whether or not you need a particle or special conjugation when coming up with your answer. We want you to be able to confidently connect い-adjectives with other parts of a sentence rather than just try to recall the correct vocabulary.