请教补充题239

239. Senator Lasker has proposed legislation requiring that employers should retain all older workers indefinitely or show just cause for dismissal.

(A) that employers should retain all older workers

(B) that all older workers be retained by employers

(C) the retaining by employers of all older workers

(D) employers’ retention of all older workers（E）

(E) employers to retain all older workers

A为何不对?是因为没有省略should吗?帮忙解答一下,谢谢先!!!