_______ he was 12, Einstein had learned advanced mathematics by himself.

A．As soon as

B．At the time

C．By the time

D．During the time

与肺癌发病关系最密切的因素是

A．职业性致病因素

B．长期吸烟

C．免疫缺陷

D．慢性肺部疾病

E．遗传因素