Adverbs of Time

[Emanuelli]

Thank you for your help. I sent a question about "used to" and "would" and I really like the answer.

I've asked a teacher about the correct structure in the following sentences:
a) Today is raining. / Today it is raining.
He told me both of them were correct, but I was wondering if you could help me understand why both of them are correct.

Other topic is that I've always heard: "My friend" and two weeks ago, I saw "A friend of mine". May I use both?
If not, could you say if I should use: "A teacher of mine", etc...
I honestly prefer "My friend..."

Thanks again.

[Casiopea]

a) Today is raining. (Not OK)
b) Today, it is raining. (OK) 'Today' functions as an adverb. It answers the question "When?". We can also move the adverb around, like this, "It is raining today."

"A friend of mine" (OK)