A man sits on a chair supported by a rope passing over a frictionless fixed pulley. The man who weighs 1,000 N exerts a force of 450 N on the chair downwards while pulling the rope on the other side. If the chair weighs 250N, then the acceleration of the chair is

• A

  0.45m / s²

• B

  0

• C

  2m/ s²

• D

  $\frac{9}{25}$m/ s²