单项选择题

Bats (are able) (to guide them) by producing sound waves (too high) for us (to hear).

A．are able
B．to guide them
C．too high
D．to hear
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I was just (falling) (sleep) last night (when) I heard a knock (at) the door.
A．falling
B．sleep
C．when
D．at
单项选择题
She was (angry), went (out), and (slamming) the door (behind) her.
A．angry
B．out
C．slamming
D．behind
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