If you must land on a beach with an oar-propelled lifeboat through a heavy surf，the recommended method is to（）.

A.keep the bow directly in toward the beach，and tow the sea anchor off the stern

B.ride in on the back of a large breaker

C.keep the bow into the seas with the sea anchor out over the bow，and row to meet the breaking waves

D.head directly into the beach by staying between the crests of the waves

一个处于稳定状态的封闭生态瓶内，要使其中的生物能长时间存活，必须提供（）

A.O₂

B.H₂O

C.足够的有机物

D.太阳能