托福词汇440题第380题

　　The smooth operation of an ant colony depends on ten to twenty different signals, most of which are pheromones(chemical signals triggering behavioral responses) .

　　The phrase "smooth operation" is closest in meaning to which of following?

　　(A) daily activity

　　(B) effective functioning

　　(C) delicate balance

　　(D) permanent location

　　答案见第2页