请教大全285 b选项还是不懂

大全285
285. Even though the state has spent ten years and seven million dollars planning a reservoir along the Ubi River, the project will have to be abandoned as a result of the river becoming so heavily polluted.
(A) will have to be abandoned as a result of the river becoming so heavily polluted
(B) is to be abandoned on account of the heavy pollution which the river received（E）
(C) had to be abandoned because the river had received such heavy pollution
(D) has to be abandoned because of the river and its heavy pollution
(E) must be abandoned because the river has become so heavily polluted

请问B错在哪里啊？是which多余吗？请nn们指点啊

但是e选项也用了状语从句啊，也不是很简洁啊？

是不是还有这样的考虑：b中强调污染这个结果，而e强调被污染这个动作，在本题中动作比结果好，即由于被污染所以be abondoned;而不是污染造成abandon

这么想有道理吗？(这两个意思似乎差别不太大)

谢谢版主

B好像确实不太顺，但是要想一下子读出这种感觉还是要靠积累啊。

路还很长……

基本明白了，但must和have to可以互换吗？是否会有逻辑意思上的改变呢？还请指点！