Before mitosis begins, what happens during S-phase? A) the sister chromosomes separates

B)cytoplasm separates

C)homologous chromosomes cross over

D) DNA replicates

A
Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. This S-phase can be referred to as "premeiotic S-phase" or "meiotic S-phase".

idk but if i had to take an educated guess i’d say a c d