Question

Scientists say it may be five years ______ it is possible to test this medicine on human patients．

A．since

B．until

C．before

D．when

Answer 1

C

本题考查连词。句意：科学家说可能还要五六年才可能将此药试验在人身上。before引导时间状语从句, 表示 “过了……就”。