Which is the topic sentence of the following paragraph?
can you imagine taking a cross-country trip with your baby sister? the trip was fun because each member of my family had different responsibilities. my mom will drive and decide where we will spend each night. my grandma will bring us lunch and read from the guidebook about different historical sites. this summer, i went on a cross-country driving trip with my mom, grandma, and little sister, and it was amazing.
question 13 options:

a)

this summer, i went on a cross-country driving trip with my mom, grandma, and little sister, and it was amazing.

b)

can you imagine taking a cross-country trip with your baby sister?

c)

my mom will drive and decide where we will spend each night.

d)

my grandma will bring us lunch and read from the guidebook about different historical sites.