Which of the following is true about the differentiability of a function at a point ??
If \( f \) is continuous at \( c \), then \( f \) is discontinuous at \( c \).
If \( f \) is differentiable at \( c \), then \( f \) is also continuous at \( c \).
If \( f \) is continuous at \( c \), then \( f \) is also differentiable at \( c \).
If \( f \) is differentiable at \( c \), then \( f \) is discontinuous at \( c \).