The doctor shares his phone number with the patients ________ they need medical assistance.

A.if only B.as if C.even though D.in case

________ birds use their feathers for flight, some of their feathers are for other purposes.

A.Once B.If C.Although D.Because

（2015·福建）        the students came from different countries, they got along quite well in the summer camp.

A. While B. Unless

C. Since D. Until

（2018·江苏）_______ you can sleep well, you will lose the ability to focus, plan and stay motivated after one or two nights.

A.Once B.Unless

C.If D.When

Tom is so independent that he never asks his parents’ opinion ________ he wants their support.

A.since B.once

C.unless D.after

（2016·天津）_____the average age of the population increases, there are more and more old people to care for.

A.Unless B.Until

C.As D.While

________ some people are motivated by a need for success, others are motivated by a fear of failure.

A.Because B.If

C.Unless D.While

The companies are working together to create ________ they hope will be the best means of transport in the 21stcentury.

A.which B.that C.what D.who

You won’t find paper cutting difficult _____you keep practicing it.

A.even if B.as long as C.as if D.ever since

If you want to lead a happy life, you’d better learn to accept life ______ it is.

A.as B.that

C.which D.where