About _________of the workers in that steel works are young people.

A．third-fifths

B．three-fifths

C．three fives

D．three-fifth

与银汞合金相比，后牙复合树脂牙体修复的缺点是（）

A.美观性能差

B.不含汞且不导热

C.聚合收缩、耐磨性能差

D.牙体预备保守

E.与牙体组织有粘结作用