Three simple harmonic motions of equal amplitudes A and equal time periods along the same line combine. The phase of the second motion is 60° ahead of the first and phase of the third motion is 60° ahead of the second. The amplitude of resultant motion is

• A

  3A

• B

  $2\sqrt{2} \mathrm{A}$

• C

  $\sqrt{3 } \mathrm{A}$

• D

  2A