单选题：Allow children the space to voice their opinions,they are di..

____ we have tried it, we can't imagine how hard it is.[ ]A. UnlessB. BecauseC. Although D. When

Jack was halfway back to the village where his mother lived _____ Mary caught up with him. [ ]A. when B. whileC. untilD. though

It's unfair! You sit there ,listening to me, _____ I stand here, teaching you. [ ]A. whenB. as C. while D. since

________ regular exercise is very important, it's never a good idea to exercise too close to bedtime.[ ]A. IfB. AsC. AlthoughD. Unless

—It's a long time________I saw you last.—Yes,and what a pity it is now that it will be a long time________we see each other again.[ ]A. before; sinceB. since; whenC. since; beforeD. when; before