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（）in computer systems.

A. useless

B. not important

C. simple but important

D. too simple to be useful

油浸变压器、电抗器安装，110kV及以上或容量30MVA及以上的油浸变压器、电抗器安装前应依据安装使用说明书编写（），并进行交底。