Which of the following statements is true of crossing-over?
a. crossing-over contributes to genetic diversity or variation.
b. the gene for eye color can be exchanged with the gene for hair color during crossing-over.
c. only one gene may be exchanged at a time during crossing-over.
d. crossing-over always results in a non-beneficial mutation.

Crossing-over contributes to genetic diversity or variation.

Crossing-over is when homologous* chromosomes exchange genes. This result in different gene combinations.

*A pair of matching chromosomes. They have the same genes but can have different versions.

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.

your answer should be c) enjoy!