请教几道语法！

salt is manufactured in quantities that exceed those of most,_ ,other commercial chemicals.

A.of all not   B.not if all are   C.are not all   D.if not all

答案是D，为什么呢？

average world temperatures have risen on half a degree celsius since the mid-nineteeth century.

答案是B，是不是要把ON去掉？

the plan connected the hudson river with lake erie by a  canal was first proposed in the late eighteenth century.

答案是A，是不是改成 TO CONNECT?

我的解释：

1 if not all 类似于if any 这个表达。这是一种省略。在这里if not all是“if the salt's quantity  doesn't exceed that of all other chemicals'"的省略

中文：如果盐的产量不比其它所有产品的产量多的化，至少也比商业化学产品多。

2 on改成by 表示增加到了某种程度，在这里是气温增加了半度。

3 connected改为connecting,分词短语做后置定语,这里表主动，所以是现在分词。

谢谢高人指点！