When it comes to____his classmates with the homework, he never feels tired.
Overpopulation is a terrible threat to the human race.Yet it is probably ____ a threat to the human race than environmental destruction.
Ladies and gentlemen,welcome to my program.____ me this evening is Dr.Gray.
While income worry is ____ rather common problem of the aged,loneliness is another problem that ____aged parents may face.
Many people can not learn any lessons from the mistakes____they get hurt somehow.
Everyone has periods in their lives_______everything seems very hard.