847. They decided to drive the cow away ______it did more damage.
A. since B. before C. after D. when
[ ]848 Scientists say it may be five or ten years ____it is possible to test this medicine on human patients..
846. ____quite recently, most mothers in Britain did not take paid work outside the home.
A. Before B. Until C. From D. Since
845. Doing your homework is a sure way to improve your test scores, and this is especially true _____it comes to classroom tests.
A. when B. since C. before D. after
844. I felt somewhat disappointed and was about to leave, ____something occurred which attracted my attention..
A. unless B. until C. when D. while
843. I have kept that portrait _____I can see it every day, as it always reminds me of my university days in London.
A. which B. where C. whether D. when
842. ______you are leaving tomorrow, we can eat dinner together tonight.
A. For B. Since C Before D. While
841. Careful surveys have indicated that as many as 50 percent of patients do not take drugs ___directed.
A. like B. so C. which D. as
840. ____that my head had cleared my brain was also beginning to work much better..
A. For B. Now C. Since D. On
839. I’ll accept my job ____I don’t have to get up early.
A. as long as B. in case C. though D. now that
838. I had just started back for the house to change my clothes, _______I heard voices.
A. as B. when C. after D. while