.We may meet all kinds of difficulties in the future, but we should be confident enough to --- any challenge.
In Britain, you must reach 18 ________ you want to drive a car.
I'll write a letter to you ________ I arrive in New York.
I told him the news ________he came back yesterday.
—Ring me up ________ you come to my house, will you? —Sure, I will.
You will fail the exam ________ you work hard.