题干
In modern times, many youths like to________others on the Internet.
A：trade in
B：trade with
C：exchange
D：exchange with
答案(点此获取答案解析）
B
In modern times, many youths like to________others on the Internet.
A：trade in
B：trade with
C：exchange
D：exchange with
为
，动点
分别在面
内，
到
的距离为
，
到
的距离为
，则