After the class,the students went out of the classroom one by one, but only Mary______.  
#104330
A
left
B
hadleft
C
wasleaving
D
wasleft
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By the time he arrived in Beijing, we _______ there for two days.
#102534
A
will have stayed
B
stay
C
have been staying
D
had stayed
He said that light ____ much faster than sound.
#100945
A
traveled
B
travels
C
is traveling
D
had traveled