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。
That proposal is essentially irrelevant ________ the issue at hand.
Neverbefore_______sorapidlydevelopingasitistoday．
Theprofessorworkedfor7hoursata________.
________，he had no time to rest.
The farming methods have been ________ improved with the invention of the new machine.
