A. a stepladder used to have four legs. B. it is dangerous to use tools C. a tripod is safer in a tool design D. workers are safer on production lines 参考答案:A 答案解析:由第三段的第一句中的“…a new design”可知,第二句中提到的a tripod ladder是a new design,相比之下,四条腿的梯子就是an old design 了,也就是说,过去