下列关于病毒的叙述，错误的是（　　）

A．外壳是由蛋白质构成的

B．内部含有遗传物质

C．不能独立生活

D．有成形的细胞核

A CO₂ extinguisher on a ship which has lost 10% of its charge must be（）.

A.used at the earliest opportunity

B.hydro-tested

C.recharged

D.weighed again in one month