What Happens Physically During the Process of Crossing Over

Multiple Choice

What happens physically during the process of crossing over?

A) Two homologous chromatids break and rejoin at random sites along the chromosome.
B) The genetic information on one chromatid is replaced by copying genetic information from a homologous chromatid without there being any physical exchange between the chromosomes.
C) Two homologous chromatids break and rejoin at precisely the same site along the chromosome so that there is no loss or gain of material on either product.
D) It is not known what occurs during crossing over.