Scientists say it may be five or ten years__it is possible to test this medicine on human patients.

问题描述:

Scientists say it may be five or ten years__it is possible to test this medicine on human patients.
A:since
B:when
C:after
D:before
选哪个?为什?

D...之前
科学家说这个药想在病人身上试验,还要等个5到10年.
A.自从
B.当
C.之后