The traffic is heavy during rush hours so they are sometimes late for school

The traffic is heavy during rush hours so they are sometimes late for school.
A. If the traffic is not heavy during rush hours, they are not sometimes late for school.
B. If the traffic were not heavy during rush hours, they would not be sometimes late for school.
C. The heavy traffic during rush hours should not make them be late for school.
D. In spite the traffic is heavy during rush hours they are not sometimes late for school