Sincewehaveafocusedsubject，weshouldnottalk________.
D
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。
The outline of rooftops and chimneys ________ against the pale sky.
Duringthepasttwodecades,researchhas________ourknowledgeofdaydreaming.
Fishis________andexpensiveatthistimeoftheyearinthisarea.
Peoplewhocan’t_______betweencolorsaresaidtobecolor-blind.