How do you do this question?

Answer:
C
Step-by-step explanation:
f"(x) < 0, which means the function is concave down at all values of x.
For any such function, within the domain of a ≤ x ≤ b, the secant line S(x) is below the curve of f(x), and the tangent line T(x) is above the curve of f(x).
Here's an example:
desmos.com/calculator/fyektbi9yl