We all know that we’ll meet all kinds of difficulties in our lives in the future. We should learn to be ________ any challenge!

______ proves that Jack is really enthusiastic and cautious.

The boss asked me to remind you of the meeting this afternoon. Don’t forget it!—OK, I _________.

What do you suppose made him so unhappy——- ________ his wallet.

My mother was doing the cleaning in the sitting room ________ the telephone rang.