____some doubt among scientists about the cause of cancer.
#92930
A
It exists
B
There exists
C
There is existing
D
It is existing
推荐题目
On turning on the computer,        .
#93452
A
Mum told me to have supper.
B
a game appeared on the screen.
C
there was something wrong with the mouse
D
I found a strange E-mail.