1 . Meanwhile, over the course of the 19th century, electricity went from mere curiosity to a basic ________ (necessary). (所给词的适当形式填空)

2 . Water is a basic _______ of life, so it is _______ to bring water when going out for a trip. (necessary) (所给词的适当形式填空)

3 . Books and pens are important ________ (necessary). (所给词的适当形式填空)

4 . Even in small companies, computers are an __________ tool.

A．necessity

B．essential

C．careful

D．elementary