The rivers will become dirtier and dirtier ______ we take action to protect them.

Don’t give up working hard,          you’ll be successful some day.

– I won’t go to the party tonight.–______ you told me you would. What’s the matter?

– This dress was last year’s style.– I think it still looks perfect ________ it has gone out of fashion this year.

—Do you like math?—Yes, it’s difficult ________ really interesting.