二、单项填空(共15分)21. ---I’m sorry I shouldn’t have laughed at you the day before. --- _________ .
Meeting my uncle after all these years was an unforgettable moment, ________ I will always treasure.
It is pretty well understood_______ controls the flow of carbon dioxide in and out the atmosphere today.
— Let’s go to a movie after work, OK?— _____________
He is said to be very rich, but I don’t understand why he is always _______.
I thought I was going to fail the exam, but I passed _______.