Linear momentum of a body is given by $\mathrm{p}=(20\mathrm{t}-3{\mathrm{t}}^2)\mathrm{kg}-\mathrm{m}/\mathrm{s}.$Then the force acting on the body at t = 1 sec,is 

• A

  6 N 

• B

  18 N

• C

  12 N

• D

  14 N