make sure that there is no blockage in the pipe 确保管道中没有堵塞
A.make sure that there is something in the pipe B.make sure that there is nothing in the pipe C.make sure that blockage is in the pipe正确答案B
make sure that there is no blockage in the pipe 确保管道中没有堵塞
A.make sure that there is something in the pipe B.make sure that there is nothing in the pipe C.make sure that blockage is in the pipe正确答案B
