Scientists warn us _____ the need to keep an eye ____ the greenhouse effect.
—Tom, you are smoking again?—______? It’s none of your business.
— May I remind you that a Mr. Smith is waiting outside, sir? — Oh, that’s right. I ______ about it.
They will fly to Washington, ______they plan to stay for two or three days.
—I’ve told Nancy many times about the meeting, but she still forget it!—I understand. Actually, anyone ______ be very forgetful at times.
— David, keep ______ in mind that you have to be home by 10 o'clock. — OK, Mom, I will.