Question

求助一道英语题

Unlike modern dams ____the water is blocked with a huge wall, Dujiangyan still lets water flow through the Minjiang River naturally. 为什么填where而不是that

Answer 1

that的话，你想的是定语从句吗？后半句不缺主宾成分,所以不是定语从句。这里where的话构成地点状语从句，这里相当于at which。 原句可变为Unlike modern dams [at which（/where） the water is blocked with a huge wall], ...

定从的话，则需改成：Unlike modern dams [that can block water with a huge wall], ...

追问

不是因为有water作主语才用that吗

追答

定语从句（名词性从句）连接词that/which 要在从句中充当成分的。
Unlike modern dams 【____the water is blocked with a huge wall】, ...
括号里是从句，water主语，后面被动语态谓语。句子意思是“水被墙挡住”句义完整，不缺主语宾语。此时可以加状语，例如本题加的地点状语。我上面说了where这里相当于at which，从句正常语序为：At the modern dams, the water is blocked with a huge wall. 译：在现代大坝的地方，水会被高墙阻隔。原句则翻译为：不同于水会被高墙阻隔的现代大坝，都江堰......
建议题主仔细阅读语法书，区分：定语从句 vs 状语从句 vs 同位语从句

Answer 2

因为dams在后面的从句中不做主语或宾语，只是描述地点的，所以用where

Answer 3

Having suffered such heavy pollution already的逻辑主语确实是the river,与主句的主语也确实不一致。但这句话是正确的。在实际语言中，时常可以遇到分词或分词短语作状语时，其逻辑主语与整个句子的主语不一致的现象，但整个句子的语法结构又是正确的情况。如：
1．相当于一个插入语
Judging from his appearance，he looks like an old doctor．