Which of the following combinations can give standing wave.
A. `y_(1)=A sin^(2)(omegat-kx),y_(2)=-A sin^(2)(omega t+kx)`
B. `y_(1)=A sin(kx-omegat),y_(2)=A cos ( omega t +kx)`
C. `y_(1)=2A cos^(2)(omega t-kx+pi),y_(2)=A[sin 2 ( omega t +kx)-1]`
D. `y_(1)=A sin (kx-omegat + 30^(@)), y_(2)=A cos ( omega t +kx - 60^(@)).`
