Resposta:

2.
a) I'm Vivian
b) We're studying in this class
c) It's mine

3.
I'm not sad: 2- Negative
I'm happy: 1- Affirmative
He's Mateus: 1- Affirmative
We aren't studying: 2- Negative
They're friends: 1- Affirmative
She isn't tired: 2- Negative

Explicação:

2. I am - I'm

We are - We're

It is - It's.

3. Percebemos se uma frase é negativa, pelo uso do "not", ou pela junção: verbo to be + not -- ex: is + not: isn't.  Sendo assim, a sequência final ficará:
(2)
(1)
(1)
(2)
(1)
(2)