—You may find the key to the math problem on page 107.—Ah, it's so simple. I wonder why I _ of that.
---- Oh, it’s raining hard outside. Do you think the milkman will arrive?---- Of course. He will come on time ________ it rains.
To keep healthy, most retired old people____ jogging as a regular form of exercise.
John, may I use your computer now?Sorry, it is not ____at the moment. It is being repaired.
Tom, look at your shirt! It requires ________.
Mr. Smith thought of himself as _______,and this accident had ________ effect on his life.