看过了前人总结却还有一点疑问：大全99，补充题249

249. Although the manager agreed to a more flexible work schedule, he said that it must be posted on the bulletin board so that both management and labor will know what everyone is assigned to do.

(A) he said that it must be posted on the bulletin board so that both management and labor will know what everyone is

(B) he said it had to be posted on the bulletin board so that both management and labor knows what everyone is

(C) he said that they would have to post the assignments on the bulletin board so that management and labor knew what everyone was

(D) he said that the schedule would have to be posted on the bulletin board so that both management and labor would know what everyone was

(E) saying that the schedule had to be posted on the bulletin board so that both management and labor would know what everyone had been

正确答案是(A), 前人们是这样总结的

must
助動詞
1.must(必須)作<情態助動詞>,相當於have to,但must強調主觀因素,而<have to>強調客觀因素。
    I must go now.
    我現在必須走。(我自己認為應該走了)
have to
助動詞
1.<have to>(必須)是<情態助動詞>,後接原形<動詞>,表示客觀條件決定不得不做某事。
    I have to go now. (我現在不得不走了)
我想，這大概就是主觀客觀的差別！

用主客观的说法来解释(A)有一定道理，但是(A)当中过去时动词said后面的间接引语从句中怎么能出现一般将来时的助动词will呢？最起码也应该变成would吧。

还是说so that后面的成分已经不属于引语内容，只是用来表示目的？但这样解释好象也不通，因为如此一来so as to好象是在说明said的目的，而不是post on the bulletin的目的了。