If $\hat{n}_1$ is the unit vector along the incident ray,$\hat{n}_2$ is the unit vector along the normal,and $\hat{n}_3$ is the unit vector along the reflected ray,then which of the following must be true?

• A
  $\hat{n}_1 \cdot \hat{n}_2 = 0$
• B
  $\hat{n}_1 \cdot \hat{n}_3 = 0$
• C
  $(\hat{n}_1 \times \hat{n}_2) \cdot \hat{n}_3 = 0$
• D
  $(\hat{n}_1 \times \hat{n}_2) \times \hat{n}_3 = 0$