— Can I pay the bill by check?

— Sorry, sir. But it is the management rules of our hotel that payment _____ be made in cash. [ ]

A. shall

B. may

C. will

D. can

海洋能源中最不稳定的一种能源是（）。

A、潮汐能

B、波浪能

C、温差能

D、盐差能

E、海流能