.P0口作输出口时,应外接____________;作输入口时,应将锁存器____________。
STC89C51单片机内部RAM有________存储空间,内部ROM有________存储空间。
单片机4个并行口既可以按________操作,也可以按________操作。若将P1.0置1,应采用的语句分别是______________和______________。
Oil is an important _____ material, which can be processed(加工) into many different chemical products, including plastics.
A. primary
B. raw
C. original
D. critical