问题
选择题
It’s said that this kind of plant only gives off this strange perfume on ________ conditions which the scientists are trying to figure out now.
A．outstanding
B．certain
C．obvious
D．ordinary
答案
答案：B
题目分析：A. outstanding杰出的，B. certain当然的，C. obvious 显而易见的，D. ordinary普通的，句意：据说这种植物只在一定的条件下散发出奇怪的香味，科学家现在正在想方法弄明白。所以选B。