請問英文a,the怎運用?

點解有時用the animal,有時用a animal
When using an animal, it does not refer to a specific animal. Therefore, use an animal when it is not an important subject or object within the sentence.
When using the animal, it means a specific animal. There should be at least 1 or 2 sentence before that already said something about the animal.
Examples below:
1. an animal
My friend told me he saw an animal in the forest.
2. the animal
Do you know what animal this is ?? It is White and have long ears.
Yes, I know. The animal is a rabbit.

a/an/the = articles in English; a kind of adjective.

The = definite article (means particular thing)
a/an = indefinit article (in general, no specific)

e.g. Let's read the book. (there is a specific book you are planning to read).
e.g. Let's read a book. (just pick one book to read, no specific one)

use an for vowels, and a for consonants.
Therefore, you should use an animal, not a animal when you are not talking about a particular one.
e.g. Ann want to buy an animal for her brother.

Use the animal, when you are talking a specific one.
e.g. The animal is very big.

2008-03-05 11:53:12 補充：
e.g. Ann wants to buy an animal for her brother.

the...指定某一樣野,或者係某一隻

an 係當個noun既開頭一個英文字母係 A, E, I, O, U 先轉做an

a 係指一樣野