问题补充：
---Was it under the tree you were away talking to a friend?
--- Sure. But when I got back there, the bike was gone.
A. that
B. where
C. which
D. while
答案：
A. that
B. where
C. which
(答案→)D. while
解析：此题很容易误以为是强调句型而选A。做好此题关键是正确理解句中的it的意思。从上下文的语境来看，it 应是代词，指代the bike，故用while 引导时间状语。句子可以理解为：“当你离开去同朋友谈话的时候，你的自行车是在这树下吗？”“当然，但当我回来时，自行车就不见了。”故选D。
