The key answer of exercise Grammar 1
The key to exercise solutions in chapter 03 - Grammar focus 2 for the textbook Cutting Edge Pre-Intermediate - Student's Book with authors Sarah Cunningham, Peter Moor and Araminta Crace from Pearson Education
Question
What form of the verb follows can, can't, have to or don’t have to? Look again at the sentences in exercise 1.
Answer
the infinitive / base form