很显然这是因为，20世纪40年代以前，吸烟年限足以引发致命癌症的男性烟民并不多(女性烟民到70年代才达到这一阈值，即吸烟年限过长引发癌症)。

That was simply because, until the 1940s, not enough men had been smoking for long enough to develop fatal cancers (women did not reach this threshold until the 1970s).

youdao

很显然这是因为，20世纪40年代以前，吸烟年限足以引发致命癌症的男性烟民并不多(女性烟民到70年代才达到这一阈值，即吸烟年限过长引发癌症)。

That was simply because, until the 1940s, not enough men had been smoking for long enough to develop fatal cancers (women did not reach this threshold until the 1970s).

youdao