● Stack is quite simple. Many computer systems have stacks built into their circuitry. The

● Stack is quite simple. Many computer systems have stacks built into their circuitry. They also have machine-level instructions to operate the hardware stack. Stack is （73）in computer systems.

（73）

A．useless

B．not important

C．simple but important

D．too simple to be useful

请帮忙给出正确答案和分析，谢谢！