A 10g bullet is fired horizontally into a 990g wooden block that rests on a frictionless horizontal surface. The bullet remains embedded, and the combined bullet-block system slides off at 2.0m/s immediately after the impact. What was the speed of the bullet just before it struck the block?
a) 100m/s
b) 20m/s
c) 200m/s
d) 198m/s