问题
选择题
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
答案
答案：D
搜题请搜索小程序“爱下问搜题”
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
答案：D