人类要生存，就得与自然环境打交道。和自然环境打交道，就应该遵守一定的规范。人类首先应该学会遵守的规范是 [     ]

①节约资源

②保护环境

③保护自然

④科学开发

A．①②③④

B．②③④

C．①②④

D．①③④

An instruction is made up of operations that (68) the function to be performed and operands that represent the data to be operated on. For example, if an instruction is to perform the operation of (69) two numbers, it must know (70) the two numbers are. The processor’s job is to (71) instructions and operands from memory and to perform each operation. Having done that, it signals memory to send it (72) instruction.

A．when

B．where

C．who

D．which