Which of the following functions represents a SHM?

• A

  Sinωt – Cosωt

• B

  $S{\mathrm{in}}^2$ωt

• C

  $S{\mathrm{in}}^3$ωt + $S{\mathrm{in}}^2$ωt

• D

  Sinωt – $S{\mathrm{in}}^2$ωt