We have decided to accept the proposal that he -------- his

A。这句话是一句同位语从句。所谓的同位语,也就是对前文提到的成分（一般是名词,类似建议、意见、观点等词）起到解释说明作用。这句话中的that 引导的从句是充当proposal（建议）的同位语。在同位语句子中经常用到情态动词should的特殊用法,即在这类句子中,should+动词原形,should经常省略。这个句子中从句部分完整的应该是he should offer his new theory,省略了should,即that he offer his new theory。decide to do 决定做某事accept proposal 接受建议。