Which of the Following Is Not Correct About Crossing Over

Which of the following is not correct about crossing over?

A) Crossing over is preceded by a process known as synapsis where homologous chromosomes attach to each other.
B) Crossing over results in greater genetic variability in offspring.
C) Crossing over is only detectable when it occurs between sister chromatids.
D) Crossing over occurs during Prophase I when homologous chromosomes line up prior to separation.
E) In humans, crossing over occurs an average of approximately two events per chromosome.