During which stage of the cell cycle does DNA replication occur?

At mid-interphase

Explanation:

The DNA replicates during the S phase of interphase, after G1 and before G2, the two growth phases. Throughout interphase, the DNA is extended, and free nucleotides have access to the strands.

During division (M phase) the DNA is condensed, so that the chromosomes are short, compact, and easily moved to the poles of the spindle.

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.