思緒集散地

twin:

For one of the two:    She is the twin.

adjective?:                The twin brothers.

Two of them:             They are the twins.

To describe a story:

use present tense.

only use past tense when something happed in past:   they were human and be tramformed to vampires.

Essay:

Always describe something you mention in paragraph when it is the first time you mention it. Even you already describe it in the last paragraph.

Letter:

Just show your problem and what you need.

"can not" is more formal than "can't"

For a letter to professior, always can't be to too cautious.

If you don't know the gender of professior, Professior (whole name or last name) is a good choice.