Which of the following normally occurs during mitosis?
a. homologous chromosomes pair.
c. unreplicated chromosomes become oriented in the center of the cell.
b. replicated chromosomes line up on the equatorial plate.
d. maternal and paternal chromatids pair

b. Replicated chromosomes line up on the equatorial plate.

Explanation:

Mitosis starts with the breakdown of the nuclear envelop and condensation of chromatids into visible chromosomes. Since DNA replication has occurred during the S-phase of interphase, each chromosome has two sister chromatids held together by a centromere. A chromosome with two sister chromatids is said to be a replicated chromosome.

Metaphase of mitosis includes the alignment of replicated chromosomes at the cell's equator. The process is assisted by the spindle apparatus. This is followed by splitting of centromere and separation of sister chromatids during anaphase.

c.           is the correct answer