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
网友回答
A. outstanding
(答案→)B. certain
C. obvious
D. ordinary
解析：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。