Which of the following quantities is always negative in SHM?

• A

  $\mathrm{F} · \mathrm{a}$

• B

  $\mathrm{v} · \mathrm{s}$

• C

  $\mathrm{a} · \mathrm{s}$

• D

  $\mathrm{F} · \mathrm{v}$

  Here, s is displacement from mean position.