The explorers failed to find the cave because it was not located      they had expected it to be.

A．which

B．that

C．where

D．what

现有0.01mol／L的下列溶液：①CH₃COOH ②NaHCO₃ ③NaHSO₄ ④KOH ⑤H₂SO₄ 按pH由小到大的顺序排列的是 (   )

A．⑤③①②④

B．③⑤①②④

C．⑤②③①④

D．④②①③⑤