Order the events that occur in dna replication

during dna replication, several proteins facilitate the unwinding of the dna double helix into two single strands. topoisomerases (red) reduce torsional strain caused by the unwinding of the dna double helix; dna helicase (yellow) breaks hydrogen bonds between complementary base-pairs; single-strand binding proteins (ssbs) stabilize the separated strands and prevent them from rejoining.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.