When in his rebellious years, that is when he was sixteen or eighteen, Frank Anderson ()going around with a strange set of people and staying out very late.

A. took to

B. took up

C. took on

D. took in

在GSM系统中，MSC之间的切换有哪些（）。

A、前向切换

B、后向切换

C、第三方切换

D、后续切回

E、后续切换到第三方