Time to put it all together!
Program your robot so that you can put the serial cable on it, and have it respond to the following commands:
f (forward): turn both motors on forward.
b (back): turn both motors on, in reverse.
l (left): turn the left motor on in reverse, and the right motor forward.
r (right): turn the right motor on in reverse, and the left motor forward.
s (stop): stop.
space: follow a line.
At the same time the robot is doing this, it should also be checking its bumpers. If either of its bumpers are pressed, it should refuse to go forward (though reverse will be fine). So, for instance, if one of the bumpers is pressed and you give it a "right" command, it should leave its left motor turned off and turn its right motor on, in reverse.
If you use polling in the serial input, you can get a maximum of 8 points (it'll be worth 10). If you use interrupts, you can get all ten points.