Which is the topic sentence of the following paragraph?

There are four people in my family. The family consists of my father, my mother, my younger sister and me. My sister is younger than me by two years. We go to school together and return together by the school bus. I am studying in class ninth and she is the student of class seventh. On return from the school, we play together. I have a pet dog. My father is working as a janitor. My mother is a housewife and looks after the household. She remains busy throughout the day. She helps me and my sister in completing our homework. Pretty soon we will be adding another member because my mom is pregnant.
Question 16 options:

a)

There are four people in my family.

b)

My sister is younger than me by two years.

c)

I have a pet dog.

d)

My father is working as a janitor.