客运索道按运载工具的高低位臵包括哪几类？
参考答案：
客运架空索道、客运缆车、客运拖牵索道。
Mary and I see each other ____, but not as often as we used to.[ ]
A. sooner or later
B. once in a while
C. in the end
D. more or less
钻井液的酸碱度代表钻井液中含酸或碱的程度
