单选题：Tom looked upon the test as an obstacle _____ his classmates..

we are not attacked by nuclear weapons, we promise that uncler no circumstances use the bombfirst but we rescrve the right to use it for counter-attack when necessary. [ ]A. As long as; we shall B. If; shall weC. So long as; shall we D. Even if; we shall

Fran is an honest girl; I say it, ________I don't like her.[ ]A. even though B. as if C. as long as D. as though

— Would you like to come to the dinner party here on Saturday? — Thank you. I'd love to, _____I'll be out of town at the weekend. [ ]A. because B. and C. so D. but

Help others whenever you can _____ you will make the world a nicer place to live in. [ ]A. and B. or C. unless D. but

People living in the desert choose to keep their ancient lifestyles and customs,_______ people in cities throw away their cultural traditions. [ ]A. when B. if C. unless D. while