Which of the following best describes the DNA content and the number of chromosomes at the end of S and M phases of the cell cycle in mitosis, if the DNA content of the cell in the beginning of cell cycle (G1 phase) is considered as C and the number of chromosomes 2N?
a. 2C and 2N for S phase; 2C and 2N for M phase
b. 2C and N for S phase; 2C and N for M phase
c. 2C and 2N for S phase; C and 2N for M phase
d. C and N for S phase; C and 2N for M phase