．—You've dropped ________ “s” in the word “acros”．

—Oh, ________ letter “s” should be doubled like this “across”．

A．a; a B．an; a C．an; the D．the; the

As ______ mountains surrounding our village are turning much greener, they have become ________ home to a large number of wild animals.

A．the; / B．the; a C．/; a D．the; the

Friendship is both ________ source of pleasure and ________ component of good health.

A．a; a B．/; / C．the; a D．a; the

Finding information in today's world is easy.The ________ is how you can tell if the information you get is useful or not.

A．knowledge B．ability

C．competition D．challenge

—He has a lot of friends who have a lot in ________ common with himself.

—Indeed.Birds of ________ feather flock together.

A．the; / B．the; a C．/; a D．a; the

It is no ________ pretending you did not know because everyone saw the whole accident.

A．use B．help C．time D．joke

—What does PM 2.5 mean?

—It's a professional ________ indicating the condition of air pollution.

A．term B．item C．number D．mark

In my brother's absence, I would like to thank all concerned on his ________.

A．behalf B．part C．business D．interest

—Do you know why Jane was so angry?

—Her roommate gave in to ________ and opened the letter addressed to her.

A．curiosity B．consideration

C．concern D．convenience

—How can I use the equipment?

—Well, just refer to the ________.

A．directions B．explanations

C．expressions D．introductions