在 Of all N1, N2... 的结构中，的确，二者属性必须相同。 但我认为这个题是没有问题的，如果Of all的后面接的是disasters，那么后面的确应该接kkgmat所说的an adverse change： Of all the disasters that threaten American agriculture, an adverse change...
在原句中 Of all the possible disasters that threaten American agriculture, the possibility 前后都是一种可能性，在逻辑上是对称的。
worry about They didn't have to worry about money. What we are worrying about is just her innocence. She worries far too much about her health. Why worry about the future? There's no sense in worrying about the boy, he'll be all right. He worries about the slightest thing.
worry over Don't worry over me, Lester. I'm all right; I'll get along. Oh, how like a woman to worry over a side-issue! She's always worrying over little things that don't really matter. He worries over the least thing that goes wrong.
sb be worried about sth
on account of and because of 在GAMT认为+DOING是不好的形式，直接加名词或者名词短语。
67、in order that 在GMAT里被认为是不正规的表达方式，就象instead of，但是不是绝对的，如果选项里有其他的合理的表达方式，例如SO THAT，就应该关注，但建议不把这个倾向作为最高优先级，还是先从其他方面排除。另外in order to通常也被认为是WORDY的，因为可以用TO直接表达，但是要比较选项。同时，SO AS TO的逻辑主语是句子主语，例如A、B，明显出现了逻辑意思上的错误，这也是需要注意的。
prohibit somebody from doing something They are prohibited from revealing details about the candidates. 没有 prohibit somebody from do something 的用法。
require sb to do require of sb that... 请注意，181就是我说的，是过去分词（表示被动的含义）才使用required of sb to do sth，当主动的时候，不使用这种方式，应该直接使用require sb to do sth! 如OG 109中的讲解。
sb require of sb to do 是 wordy的表达方式，直接使用sb require sb to do.
require of sb to do 经常用在被动的方式或者说过去分词的形式来修饰名词，例如 sb/sth required of sb to do is/does......，以前讨论过，另外OG里还有一题，你用required of 搜索一下OG。
区别就是so as to只用于简单的系表结构中，句子主语和to do 的主语相同，且不能倒装。 而so that就把它要广泛地多，从句和主句中的 主语，时态，结构等均可变换，关键的一点：可以用于而且经常用于倒装结构。
介词短语与从句修饰的意思不一样： twins with the same genetic endowment 翻成汉语的意思是：具有相同基因构成的同卵双胞胎。 言外之意是还有“不具有相同基因构成的同卵双胞胎。”
而 involves identical twins who have the same genetic endowment 的意思是：涉及同卵双胞胎，而（同卵双胞胎）具有相同基因构成。 也就是定语从句是对其修饰对象的解释，而非限定。 或者说定语从句是与其修饰对象可以划等号，而介词短语却不可以。
字典上只有demanded that，而没有demanded sb to do的用法：
Angry demonstrators demanded the resignation of two senior officials. demand to
know/see/have etc something I demand to know what's going on.
demand that They demanded that the military government free all political prisoners.
demand something of somebody It seemed that no matter what she did, more was demanded of her. 'Where are you going?' she demanded angrily. 作者: bloomingdales 时间: 2008-2-12 21:33
