It never _____ humans until the mid1990s that some animals can be cloned.
#92718
A
occur
B
is occurred
C
occurred to
D
occurred
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— the team finished most of their research work?—Yes, but the rest rather difficult.
#93550
A
Has, are
B
Has, is
C
Have, are
D
Have, is
—Haven’t seen Lucy recently. What’s happened?—Oh, it’s more than two months ______ she worked here.
#92295
A
before
B
after
C
since
D
when
AIDS is said_______ the biggest health challenge to both men and women in the earth over the past four years.
#91954
A
that it is
B
to have been
C
that it has been
D
to be
Marry was holidaying with her family in a wildlife park______she was bitten on the leg by a lion.
#95127
A
while
B
when
C
before
D
after