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.