Help me please.

1. In the past, people used to write a letter to each other. Now they send e-mails to each other.

2. Do people in the past used to write with a ball point pen? Now we use it a lot.

3. My mother used to not wash my clothes when I was a student.

4. Bold used to be thin, now he is fat.

1. In the past, children used to do sums with an abacus. Now they use a calculator.

2. Before, children used to not ride a school bus to go to school. Now they go by bus.

3. Do they used to live in a small house?

4. Zaya used to not have a lot of books before.

Explanation:

Just insert "used do" and "do" verbs.

a. is the correct answer