As we all know．____life is hard for any of us. If we live___ happy life，we must all work harder.

A．／：／

B．／；a

C．a；／

D．a；a

RISC的关键技术是寄存器窗口重叠技术，这项技术很好地支持过程调用和返回操作。这里所谓的重叠是指

A． 全局寄存器与高位寄存器重叠

B． 全局寄存器与局部寄存器重叠

C． 高位寄存器与低位寄存器重叠

D． 高位寄存器与局部寄存器重叠