$1 \, \text{atomic mass unit (amu)}$ is equal to:

• A
  $\frac{1}{25} \times (\text{mass of } F_2 \text{ molecule})$
• B
  $\frac{1}{14} \times (\text{mass of } N_2 \text{ molecule})$
• C
  $\frac{1}{12} \times (\text{mass of one } C-12 \text{ atom})$
• D
  $\frac{1}{16} \times (\text{mass of } O_2 \text{ molecule})$