John was working on his assignment when he saw his ...

★ Past Tense and Neutral

John was working on his assignment when he saw his friend _________ over a brick on the floor.

A. trips

B. tripped

C. tripping

D. trip

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Alex saw the lost toddler __________ sadly while concerned passers-by were trying to comfort her.

A. sob

B. sobbing

C. has sobbed

D. had sobbed