此处总结一下what从句做主语时，谓语动词的单复数情况：
当what在从句中充当主语时，主句谓语动词的单复数由what引导的主语从句中的谓语动词的单复数决定。例如：
(1) What is difficult to understand IS(看前面从句的谓语动词is) A.
(2) What are difficult to understand ARE（看前面从句的谓语动词are） A and B.
当what在从句中充当宾语时，主句谓语动词的单复数由主句的表语/宾语决定。例如：
What his father left him ARE(看主句宾语或者表语，即 a few books) a few English books.
leaking its cargo of 750,000 gallons into the ocean, while causing the pollution of the city's beaches.
while表示leaking 和causing的并列，都是状语修饰主句动作，逻辑主语都是主句主语，表示同时，
插入语必须头尾用两个逗号将其隔开
，98 percent of men and 75 percent of women who were born in the country, by the time they reached adulthood had been attacked by the birds
adulthood少了逗号
原句：The influence of Jane Austen is more apparent nowhere in early American literature than in the novels of James Fenimore Cooper.
完全倒装句：Nowhere in early American literature is the influence of Jane Austen more apparent than in the novels of James Fenimore Cooper.
1) 宾语从句强调整体, 谓语+宾语结构只强调宾语
(A) of there being代替that同位语从句表达复杂,笨拙并且不符合习惯.
(B) 错误同A选项
(C) 错误同A选项
(D) 正确, 用that同位语从句清楚地解释了generalization的内容
(E) In the phrase 'little of X', the X has to be a singular quantity. If it's plural (like 'differences'), then you have to use few.
eg. There was very little food left over at the end of the party.
There were very few crab cakes left over at the end of the party.——即little of + 不可数名词，few +可数
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破折号单独用时表示后句是对前句的解释说明，不能用来分割主语和系表结构。当然，破折号在成对使用时，可以同逗号一样用于隔开插入语