The velocity 'V' of a particle varies with distance 'x' and time 't' as V=Asin(Bx)cos(Ct) when A,B,C are constants, then ABC will have the dimensions of:
A has the same dimension as V ⇒A=LT−1
Ct and Bx has the same dimension as M0L0T0
i.e it should be dimensionless.
⇒Bx=M0L0T0
B=M0L−1T0
Ct=M0L0T0
⇒C=M0L0T−1
So,ABc=(L1T−1)(M0L−1T0)(M0L0T−1)=M0L0T0
Out of the above option, only strain is dimensionless.
Hence, option D is correct.