5. The function $f(x)=\left\{\begin{array}{ll}1-5^{-x} & x \geq 0 \\ 5^{x}-1 & x<0\end{array}\right.$, then the function is
A. Monotonically increasing function, odd function
B. Monotonically decreasing function, even function
C. Monotonically increasing function, even function
D. Monotonically decreasing function, odd function
A )
Answer: According to the definitions of monotonicity and odd/even properties, the function is a monotonically increasing odd function. The correct answer is A.