1- هنگامیکه برای اولین بار به کسی یا چیزی اشاره می‌کنیم از a یا an استفاده می‌کنیم. اما وقتی که به همان چیز دوباره اشاره می‌شود، باید از the استفاده کرد:
I bought a new shirt yesterday. But my wife thinks the shirt doesn't fit me.
(دیروز یک پیراهن نو خریدم. ولی همسرم فکر می‌کند که آن پیراهن اندازه من نیست.)
Once I had a really big dog. But the dog wasn't very useful, so I gave the dog toa friend.
(زمانی یک سگ خیلی بزرگ داشتم. اما آن سگ خیلی مفید نبود، برای همین سگ را به یک دوست دادم.ا)
2- وقتی که به یک چیز مفرد اشاره می‌شود از a یا an استفاده می‌کنیم. در این حالت همان معنی one یا «یک» را می‌دهد (در مقایسه با three، two و ...):
I'd like an apple and two oranges.
Yesterday I bought three pencils and a notebook.
3- در اصطلاحات عددی خاص:
a half | یک دوم | |
| a third | یک سوم | |
| an eighth | یک هشتم | |
| a couple | یک جفت | |
| a dozen | یک دوجین | |
| a hundred | صدتا | |
| a thousand | هزارتا | |
| a million | یک میلیون |
4- هنگام اشاره به یک عنصر خاص از یک گروه یا طبقه:
الف. همراه با اسامی شغلها:
She's a doctor.
My father is a teacher.
Are you an engineer?
ب. همراه با ملیتها و مذاهب:
I'm an Iranian.
You are a Chinese.
She is a Catholic.
5- همراه با کلمات و اصطلاحات مربوط به مقدار و کمیت:
a few (of) | a lot (of) |
a little (of) | a (great) deal (of) |
a bit (of) | a number (of) |
6- همراه با اسامی مفرد قابل شمارش و پیش از کلمات what و such:
What a beautiful day! (چه روز زیبایی!)
What a strange friend you have! (عجب دوست عجیبی داری!)
Such a pity! (چه حیف شد!)
First of all, to make the difference between 'under' and 'below'. Both of these words can mean 'in a lower position than', so there's a sense in which they mean the same thing. But we use them sometimes in different circumstances, for example, if you're talking about something being covered by something, we use 'under'. So, 'I hid the key under a rock'. Or, 'officials said there was nothing under President Bush's jacket'.
You use 'below' when you're talking about something that's not physically immediately under, or not necessarily immediately under. So you say, 'below the surface of the water'. That might be anywhere below the surface of the water, not necessarily just touching it. Or, 'twenty miles below the earth's surface', definitely not immediately under it. And, by extension, we say things like, 'below the poverty line'.
We also use 'under' when we're talking about 'younger than' or 'less than'. So, 'under a dozen times', 'under the age of ten'. Whereas we use 'below', if we're visualising a kind of vertical scale. So, 'below sea level', 'below average', 'an IQ below 80', 'radio waves below 22 kHz'.
There are a number of fixed expressions, so, for example, a lot of expressions about what's happening while something else is going on, or because of certain conditions, or controlled by something or someone. So we say, 'under construction', 'under fire', 'under attack', 'under arrest', 'under these conditions', 'under scrutiny', 'under pressure', 'under the Ceausescu regime'. All of those form a kind of a family.
So what about 'beneath'? Well, 'beneath' is basically more literal, or formal, and we use it in many of the same senses. But there are lots of fixed phrases, and so what you want to do is just read a lot and note when one is used and when the other is used. I hope those will give you some general guide lines, and that you'll enjoy keeping learning about these
three fascinating words.