Open the brackets, put the verb in the correct form in the sentence: “Why are you doing all those exercises now? You could (to do) ... them yesterday.”

Why are you doing all those exercises now? You could have done them yesterday.

После модального глагола could для выражения возможности в прошлом используется конструкция could have + причастие прошедшего времени: do → done.

Ответ: have done