4. Among the following functions, the one with minimum positive period $\pi$ and whose graph is symmetric about the origin is\\
A. $\mathrm { y } = \cos \left( 2 x + \frac { \pi } { 2 } \right)$\\
B. $y = \sin \left( 2 x + \frac { \pi } { 2 } \right)$\\
C. $y = \sin 2 x + \cos 2 x$\\
D. $y = \sin x + \cos x$\\