The correct option is C the amount of DNA doubles and chromosome number remains constant
Cell cycle includes an orderly sequence of events during which cell synthesises cellular contents, duplicates its genome and eventually divides forming daughter cells. Cell cycle includes two phases - interphase and mitotic phase.
Interphase is a non dividing phase during which cell prepares to divide. Interphase includes G1, S and G2 phases.
During S phase (synthesis phase), DNA undergoes replication and makes a copy of itself. Hence, the content of DNA doubles during S phase. Each chromosome after DNA replication will have two chromatids and there is no change in the chromosome number. Hence, the chromosome number remains constant during S phase.