题目

.Modern agriculture has greatly developed and nowadays animals are usually raised in _____        we call factory farms. As a result of this, lots of labour is saved. A. which                      B. where                    C. what                 D. how  答案：C下面说法中正确的是：A．马德堡半球实验是用来大气压数值的一个实验B．托里拆利实验中的玻璃管内的汞面上受到大气压强C．同一地点的大气压不是固定不变的D．大气压的方向一定是竖直向下的