Assertion (A): Nitrogen cools when expanded through a throttle at room temperature. Reason (R): The inversion temperature of nitrogen is about $621\mathrm{K}$, well above room temperature. Choose the correct option.

1. ABoth A and R are true and R is the correct explanation of A
2. BBoth A and R are true but R is not the correct explanation of A
3. CA is true but R is false
4. DA is false but R is true