Two sound waves (expressed in CGS units) given by ` y_(1)=0.3 sin (2 pi)/(lambda)(vt-x) and y_(2)=0.4 sin (2 pi)/(lambda)(vt-x+ theta)` interfere. The resultant amplitude at a place where phase difference is ` pi //2 ` will be
A. `0.7 cm`
B. `0 .1 cm`
C. `0.5 cm`
D. `(1)/(10) sqrt(7) cm`