The key to exercise solutions in chapter Unit 51 - Auxiliary verbs for the textbook English Grammar in Use with authors Raymond Murphy from Cambridge University Press
Question
Complete each sentence with an auxiliary verb (do / was / could etc.). Sometimes the verb must be negative (don’t / wasn’t etc.).
Answer
were
doesn't
was
will
am; isn't / 'm not; is / can; can't / can't; can / am; can't / can't is