A particle moves along a straight line so that its velocity v(t) and acceleration a(t) satisfy the following sign chart.
• v(t)>0 for 0<t<3
• v(t)<0 for 3<t<6
• a(t)<0 for 0<t<2
• a(t)>0 for 2<t<6
On which time interval is the particle speeding up?
a) 3<t<4
b) 0<t<2
c) 2<t<3
d) 0<t<3