21．He get here on time because there’s always traffic jam at this rush hour.
A．can’t B．mustn’t C．shouldn’t D．needn’t
22．—Can you give me the right answer?
—Sorry, I . Would you repeat that question?
A．hadn’t heard B．haven’t followed
C．don’t catch D．wasn’t listening
23．All the passengers object to transferring to the next flight they are given a proper explanation.
A．though B．unless C．if D．so long as