单复同形的情况
*英语中有少数名词，复数形式与单数形式相同，如：
He is as timid as a sheep.他象绵羊一样怯懦。
We are grazing the sheep in the next field.我们在旁边的地里放羊。
The speed of this aircraft is very high.这架飞机的速度非常快。
All aircraft must fuel before flight.所有飞机飞行前都必须加油。
The dog roused a deer from the bushes.狗惊起了丛林中的一只鹿。
Male deer usually have horns on their heads.公鹿头上通常有角。
My goldfish has died.我的金鱼死了。
The fisher drew in the net and found two goldfish in it.
渔夫收了网，发现有两条金鱼在里面。
常见的单复同形的名词有：
a. 某些动物的名称：
bison(野牛) deer grouse(松鸡)
cod(鳕鱼) fish goldfish
halibut(大比目鱼) mullet(胭脂鱼) salmon(鲑鱼)
moose(麋) reindeer(驯鹿) sheep(绵羊)
shellfish(贝壳动物) trout(鳟鱼) whitebait(银鱼)
b.craft及由craft构成的词：
aircraft craft(船) hovercraft(气垫船) spacecraft(宇宙飞船)
c.表示某国人的名词：
I’m proud I am a Chinese.我骄傲我是中国人。
The Chinese eat with chopsticks.中国人用筷子吃饭。
His wife is a Vietnamese.他妻子是越南人。
The Vietnamese are noted for their cookery.越南人因其烹调而出名。
It was invented by a Swiss.这是一位瑞士人发明的。
The Swiss did not take their fate lying down.瑞士人并不甘心接受被征服的命运。
Tips: 不能说an English，要说an English man。有些词则要加-s，如Scot(s)。
d.还有一些其他单、复同形的名词(斜体部分)：
This rare bird has become an endangered species.这种珍禽已成为濒临灭绝的物种。
There are over 200 species of fish.有二百多个品种的鱼。
…
*有某些词有特殊情况：
fruit：通常作总称或集体名词，没有复数形式：
I like fruit and vegetables.我喜欢水果和蔬菜。
This pudding has two pounds of fresh fruit in it.这个布丁里有两磅鲜果。
在表示某种水果时可有复数形式：
The potato is a vegetable, not a fruit.马铃薯是一种蔬菜，不是一种水果。
The country exports tropical fruits.该国出口热带水果。
用于抽象或比喻义时也可有复数形式：
They enjoy the fruits of their hard labor.他们享受自己辛勤努力的成果。
hair：通常作单数，是头发或动物毛发的总称：
She was slender and had long dark hair.她身材苗条，有一头长长的黑发。
My hair has grown very long.我的头发长得很长了。
但表示一根头发或毛时可有复数，用作可数名词：
There are a few hairs in the book.书里有几根头发。
He had a few grey hairs.他有几根灰白色的头发。
*有一些名词有两种复数形式，如：
The herring(s) usually live in large shoals. 鲱鱼通常生活在大的浅水区。
Zebra(s)are a more difficult prey.斑马是一种比较难捕获的猎物。
另有一些带-s词尾的词，通常用作单数(斜体部分)：
The accident took place at a crossroads.事故就发生在一个十字路口。
The business cycle is a series of peaks and troughs.商业周期就是淡旺期交替。
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