Function represents SHM :
(i) for any value of A, B and C (except C = 0)
(ii) if A=- B; C = 2B, amplitude =
(iii) if A = B; C = 0
(iv) if A = B; C = 2B, amplitude
For (a) : For any value of A, B and C (except C = 0), it represents SHM
For (b) : If A = -B and C = 2B, , x = B cos t + B sin 2 t which is SHM.
For (c ): If A=B,C =0, x= A = constant Not a SHM.
For (d) : If A=B,C =2B, x = B+B sin which is SHM.