I can still remember that it is since the 1990’s, _____ we began to use cell phones,_______ the number of mobile users has greatly increased．
#79738
A
while; when
B
when; what
C
before; that
D
when; that
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it is normal for parrots to talk, Einstein, a small bird, is unusual in that whenever she hears a new word or sound, she repeats it over and over until she masters it.
#30576
A
As
B
When
C
While
D
Since
Between the two periods of classes is a break,_____we can have a short rest.
#79676
A
then
B
where
C
when
D
Which
They had just finished the work _______ there was another one waiting for them.
#31462
A
while
B
when
C
as
D
since
．In Australia there are over 140 species of snakes, many of ______ are extremely dangerous.
#34499
A
which
B
that
C
them
D
those