Although the causes of cancer_____, we do not yet have any practical way to prevent it.

A．are being uncovered

B．have been uncovering

C．are uncovering

D．have uncovered

Leber遗传性视神经病变的遗传方式是

A．X-性连锁隐性遗传

B．常染色体隐性遗传

C．常染色体显性遗传

D．线粒体DNA遗传

E．以上都不是