问题补充：
By then there may be only standing room on the earth.A where to goB where to livec where to livingDwhere to stand 为什么啊
答案：
DBy then there may be only standing room on the earth.
=== By then,on the earth there may be only room for you to stand in because there will be many many many many people on this planet.----------- 只有站的地方,没有住的地方.
