Which sentence uses an effective transition?

A. So Marcus's computer stopped working due to he had to get a new laptop
B. Lots of kids signed up for the race as the school needed to make three different time slots
C. Leila lost her favorite necklace, consequently she found it in the garbage can
D. I signed my puppy up for obedience classes because she chewed up all my shoes

B. Lots of kids signed up for the race as the school needed to make three different time slots.