Hi, Hi, Here is a good grammar rule to learn regarding when to us "a" and "an": Use "an" if the next word starts with a vowel sound. Use "a" if the next word does not start with a vowel sound. The use of contractions (he's instead of he is, etc.) is fine in English writing; the only time it is not recommended is when you are writing an academic paper.

She's a teacher. This sentence is right. correction: He's an engineer They're doctors It's a dog

"She's a teacher" is correct. The others should be: "He's an engineer." "They're doctors." "It's a dog." The sentences above are how they would be used in speech. In all of these cases, it would be more proper to write formally: "He is an engineer" "She is a teacher" "They are doctors." "It is a dog."

''She's a teacher'' is the only correct sentence. The rule is, if followed by a vowel you use 'an' and if followed by a consonant you us 'a'. So it should be: He's AN engineer. She's A teacher. They're doctors (the an or a is not necessary, but you must use the plural) It's A dog.

Here is a hint: "An" must come before singular nouns that start with a vowel, or for some people a vowel sound (such as: an herb, when the "h" is not pronounced).