Every year my family and my best friend’s family go to the beach so we can relax and have fun. each october our parents start looking for a place to stay at the beach. we don’t go to the same beach every year, so there is always something new and exciting to see. once december comes, we have our reservation made and my parents tell us on christmas morning the details about the trip. then i start getting excited about the trip, so does my best friend.

which sentence contains an error using so?
a.) every year my family and my best friend’s family go to the beach so we can relax and have fun.
b.) we don’t go to the same beach every year, so there is always something new and exciting to see.
c.) then i start getting excited about the trip, so does my best friend.