Which correctly describes crossing over

Hello. This question is incomplete. The full question is:

"Which correctly describes crossing over?  A)the process whereby nonsister chromatids exchange genetic material  B)the process whereby homologous chromosomes are pulled to opposite poles of the cell  C)the process whereby sister chromatids are pulled to opposite poles of the cell  D)the process whereby homologous chromosome pairs align randomly along the metaphase plate"

A)the process whereby nonsister chromatids exchange genetic material

Explanation:

Crossing over is a phenomenon that involves homologous chromatids. They break at some points and, in the sequence, there is an exchange of corresponding pieces between them. It is worth noting that the exchanges cause the emergence of other gene sequences along the chromosomes. Thus, if there are several genes combined on a chromosome, after crossing the combination can be changed.

This process occurs during prophase I of meiosis cell division. Because of this characteristic, crossing increases genetic variability.

b. the carbon cycle ensures living things have a source of hydrogen