2. Which of the following functions is an odd function? A. $y = \sqrt { x }$ B. $y = | \sin x |$ C. $y = \cos x$ D. $y = e ^ { x } - e ^ { - x }$
2. Which of the following functions is an odd function?\\
A. $y = \sqrt { x }$\\
B. $y = | \sin x |$\\
C. $y = \cos x$\\
D. $y = e ^ { x } - e ^ { - x }$