It was not until 1911, _______ the first vitamin was identified, _______ people realized the importance of it．
#85155
A
when; which
B
when; that
C
that; which
D
that; that
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It is the protection for the trees___________ really matters, rather than how many trees are planted.
#85499
A
what
B
that
C
不填
D
which
It is the educational system, rather than the teachers, _______ is to blame for the students’ heavy burden nowadays.
#85156
A
who
B
this
C
that
D
whom
It was 80 years before Christopher Columbus crossed the Atlantic Zheng He sailed to East Africa
#85222
A
when
B
that
C
after
D
since