The point represented by the complex number $2-i$  is rotated about the origin through an angle $\frac{\pi }{2}$  in the clockwise direction, the new position of the point is:

(a) $1+2i$     

(b) $-1-2i$    

(c) $2+i$     

(d) $-1+2i$    

$\mid z_1+z_2\mid \ge \mid \mid z_1\mid -\mid z_2\mid \mid$