假设由CALL指令调用的某子程序使用段内返回指令RET4，问．该予程序执行到 RET4指令时( )实现返回操作

A．返回到CALL指令下面一条指令继续执行主程序

B．按照(SP)和(SP+1)中存放的地址执行返回操作

C．按照(SP+4)和(SP+5)，中存放的地址执行返回操作

D．返回到CALL指令下面第4条指令继续执行主程序

In an open lifeboat，the lifeboat compass is usually（）.

A.placed in a fixed bracket when being used

B.clamped to any position convenient for the coxswain to see it

C.permanently mounted on the lifeboat's centerline

D.mounted in the center of the boat to eliminate deviation