Sincewehaveafocusedsubject，weshouldnottalk________.
A、atonceD
译文：既然我们已经有了命题， 我们就不应漫无边际地交谈。 此题考查对固定短语的掌握情况。 at once 立刻; at hand在附近，在手头，即将发生; at intervals 间或，不时; at random 随便，任意。
When _______, water will be turned into steam.
It has been found that a strong ________ help overcome the effects of distraction.
Theoceansdonotsomuchdividetheworld_______uniteit
Duringthepasttwodecades,researchhas________ourknowledgeofdaydreaming.
Robotsdifferfromautomaticmachines________aftercompletionofonespecifictask，theycanbereprogrammedbyacomputertodoanotherone.
