新概念英语4学习笔记：第18课 Porpoises
本文选自吴应时的《应时新概念英语4》，是学习新概念英语第四册的辅助学习笔记，提供知识点精讲及解析，想知道具体都有哪些内容，那就一起来看看吧。
第一段语法符号详解：
1. There has long been a superstition that porpoises will save men or protect them…
复合句，主句为 there be 句型，然后有一个 that 引导的同位语从句. 该从句为并列句，主谓宾结构.
2. biologists have pointed out that it is a mistake to credit…
复合句，主句为主谓+that 引导的宾语从句.该宾语从句亦是复合句，包括 however 引导的让步状语从句，以及主系表结构的主句，主句中动词不定式作真正的主语.
3. when…they have done it…
复合句，when 引导时间状语从句在前，为主谓宾结构. 主句为主谓宾结构，主句中 as 引导的方式状语有省略，as they did in riding the bow waves…
4. some porpoises were photographed…
简单句，被动语态的主谓结构，加上主语补足语作补充说明. working like beavers 为伴随状语. Someone photographed some porpoises
5. If…they have protected humans…, it may have been because…and because…
复合句，if 引导的条件状语从句为主谓宾结构，其中包括 as 引导的定语从句. (2.2.1)
主句为主系表结构，为并列句，and 连接两个表语从句. 表语从句均为主谓宾结构.
6. Porpoises and sharks are enemies.
简单句，主系表结构.
7. It is possible that… a battle ensued…
复合句，it 作形式主语. 真正的主语由 that 引导的主语从句担任，该主语从句为主谓结构.
第二段语法符号详解：
1. Whether…the porpoise is intrigued with anything that is…
复合句，主句为主谓宾结构，宾语 anything 由 that 引导的定语从句修饰. 开头是 whether 引导的让步状语从句. 该从句为主系表结构.
2. They are after the turtles who…
复合句，主句为主谓宾结构，be after 为动词词组. who 引导的定语从句为主谓宾结构，修饰 turtles.
3. One young calf enjoyed raising… and shoving…
并列句，主句为主谓宾结构，两个动名词 raising 和 shoving 作 enjoy 的宾语.
4. a young porpoise may be seen…
简单句，主句为被动语态的主谓结构，同样的，后面的补语在非被动语态中作宾语补足语，而现在则作该被动语态中的主语补足语.
by 引导的方式状语本身比较长，是并列结构，可以看成是 by sticking and by pushing.
for dear life 为 for one's life 的变体，拼命之意.
5. This is not easy and (this) may require two porpoises…
并列句，首句为主系表结构，后句省略了主语，为主谓宾+宾补结构.
6. the first porpoise swoops down…and butts…
并列复合句，主句为主谓宾结构，后句省略了主语.
as 引导的时间状语从句为主谓结构.
7. This knocks down the turtle…
简单句，主谓宾结构，谓语由动词词组担任.
8. He recovers his equilibrium than the next porpoise comes along and hits…
复合句，主句主谓宾结构.
从句为并列句，主谓宾结构，第二句省略了主语，(the next porpoise) hits him another crack 双宾语，him 为间接宾语，another crack 为直接宾语.
这里是 no sooner…than 结构的时间状语从句，语法上，主句用过去完成时，从句用一般过去时. 本句可写作：No sooner had he recovered his equilibrium than the next porpoise came along and hit him another crack.
9. the turtle has been butted…
简单句，主谓结构.
10. He is satisfied to try… but a porpoise knocks him…
并列复合句，but 分成前后两句.
第一句为主谓宾结构.
第二句为 as soon as 引导的时间状语从句，以及主句为主谓宾+宾补结构.
11. The turtle gives up and the game is over…
并列句，第一句主谓结构，第二句主系表结构.
