——May I go to play football with Mike now, Dad? ——No, you can’t go out ______ your homework is being done.
By using ears one can tell the direction ____ a sound comes.
I don’t believe the reason ____ he has given for not coming to the lecture.
In the forest we observed some trees ____the leaves were black with disease.
I often think of the years ____ I worked with the foreigners, ____ has had a great effect on my later life.
He expressed his hope ____ he would visit China again the next year, and this was the very hope ____ he expressed as soon as he arrived in the country.