Crossing over occurs at the four-strand stage when two homologous chromosomes, each consisting of a pair of sister chromatids, are paired. Each crossover involves just two of the four strands and generates two recombinant strands.
Hope this helps!
I think I found your question online and if the questions are the same, the answers would be A. B. and C. Once again, you do not have to take this answer because I am unsure if I found the same chart that you have.
Ribosomes synthesize proteins
