Though scientists get closer to understanding why we age， the reason for different aging rates among individuals remains only __________ understood．
A. concretely B. thoroughly
C. vaguely D. flexible
The study， from academics at Harvard， claims __________ the first clear evidence showing that when temperatures go up， school performance goes down．
A. to have produced B. to produce
C. producing D. being produced
Using AI， many companies are now conducting experiments that__________ possible just a few years ago．
A. would have been B. might have been
C. shouldn't have been D. couldn't have been
﹣﹣﹣_________ makes your son feel blue today？
﹣﹣﹣_________ to watch his favourite cartoon Paw Patrol．
A. What it is that； To be forbidden
B. What is that； Forbidden
C. What is it that； Being forbidden
D. That is what； Having forbidden
Granny always keeps her cellphone switched off _________she's expecting a call．
A. Since B. unless
C. once D. when
﹣﹣﹣Why not turn to Kevin？ He saw what happened， so his is the only _________ account．
﹣﹣﹣The problem is that he has refused to say anything about the accident．
A. tentative B. controversial
C. authentic D. arbitrary
