As technological advances put more and more time between early school life and the young person's final access to specialized work, the stage of______becomes an even more markedand conscious period.

A．adolescence

B．adjacency

C．advantage

D．adventure

患儿男，7岁，因发热、鼻出血、面色苍白、虚弱无力而住院。经血象和骨髓象检查被诊断为“急性白血病”

可能成为该病的主要致病因素是

A．血液病

B．家族遗传

C．病毒感染

D．电离辐射

E．化学物质