Determine the correctness or otherwise of the following Assertion [a] and Reason [r]. Assertion: Biaxial minerals can be pleochroic in three shades. Reason: Biaxial minerals have three refractive indices.

• A. Both [a] and [r] are true and [r] is the correct reason for [a]
• B. [a] is true but [r] is false
• C. [a] is false but [r] is true
• D. Both [a] and [r] are true but [r] is not the correct reason for [a]