He was riding to school   he was hit by a car this morning. 
#41376
A
while
B
when
C
as
D
so
推荐题目
As long as the laws of nature ______, there will be tornadoes.
#68427
A
exist
B
are existing
C
will exist
D
existed
Can you make sure _____________ the gold ring? 
#74043
A
where Alice had put
B
where had Alice put
C
where Alice has put
D
where has Alice put
He never speaks to others until ______.
#67931
A
he speaks
B
spoken to
C
he is spoken
D
he speaks to