Homologous pairs separate in meiosis , and sister chromatids separate in meiosis .

Homologous pairs separate in first round of meiosis or meiosis 1

However,

sister chromatids separate in second round of meiosis or meiosis 2.

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.