单选题
______ at the outset, ______ instead of shifting thing about may be pheromones released when they reach committee size. A. The stimuli set them off ... build collectively B. The stimuli that set them off ... building collectively C. The stimuli setting them off ... they build collectively D. Being set off by stimuli ... their building collectively
【正确答案】
B
【答案解析】[解析] stimuli是主语，定语从句that set them off at the outs跟在其后，第二个横线处应为分词短语building collectively作状语。由此可知本题答案为B。