Tom has been a vegetarian ____principle for years .
The time has come _____ we make extensive use of nuclear energy.
The two main print media is : （）
Do you know the name of that _____ insect?
Sit back and reflect on ______ it is that you do best and what you enjoy.
The ____of AIDS has led to an expansion in research seeking a cure.
Mario: Your beloved teacher has arrived here, Nina.
Nina: I______ she ______ until tomorrow.
Your sister _______to visit you quite ofen,didn't she?
You do not want to squander time and effort on a position ______is not a good fit.
Let's go swimming,_______?