下列哪种方法不属于人工下管方法。（）
A.压绳下管。
B.后蹬施力下管法。
C.肩扛下管法
D.木架下管法。
参考答案：C
Clean water and fresh air are essential for our daily life, _______ we can’t live.
A．by which
B．without which
C．that
D．on which
