Change the sentences to past

1. We are students this year.

 a.We was students last year.

b. We were students this year.

c. We are students last year.

d. We were students last year.

2. I'm cooking right now.

a. I'm cooking last night.

b. I was cooking last night.

c. I cooked last night.

d. I'm cooked last night. 

3. I'm studying right now.

a. I study last night.

b.I was study last night.

c.I studied last night.

d. I'm studied last night.

4. Class is boring.

a. Class was boring.

b. Class it was boring.

c.Class are boring.

d. Class were boring.