Which Aspect(s)of Chromosome Behaviour Is/are Primarily Responsible for the Tremendous

Multiple Choice

Which aspect(s) of chromosome behaviour is/are primarily responsible for the tremendous amount of genetic variability associated with sexual reproduction?

A) Segregation of sister chromatids at anaphase II of meiosis
B) Segregation of homologous chromosomes at anaphase I of meiosis
C) Crossing-over between homologous chromosomes during prophase I of meiosis
D) Independent alignment of different homologous pairs on the metaphase I spindle
E) Both crossing-over between homologous chromosomes during prophase I of meiosis and independent alignment of different homologous pairs on the metaphase I spindle contribute to genetic variability