单项选择题 牛的环形泰勒虫“石榴体”阶段寄生部位是

单项选择题 顶入法是指用专用的（ ）设备在成型孔中直接顶入管道的方法。 A. 开挖 B. 顶管 C. 盾构 D. 钻进

单项选择题 Flow control is one of the basic functions of the data link layer. Regarding flow control, which one is correct among following statements? A、Only the data link layer has flow control B、Not only the data link layer has flow control, but the flow control objects of each layer are the same C、Not only does the data link layer have flow control, but the flow control objects of each layer are different D、None of the above is right