问题
选择题
________ these experiments were successfully completed would we think of going into humans.
A．If only
B．Only if
C．So that
D．Even if
答案
答案：B
题目分析：句意：只有这些实验完全成功以后，我们才会考虑把它应用于人类。根据“would we think of going into humans.”可知这个句子使用了部分倒装，所以用only+状语从句位于句首，选B。