In order to identify hazards early and avoid last minute moves, you should scan the road seconds ahead of your vehicle.
a. 5 to 10

In order to identify hazards early and avoid last minute moves, you should scan the road 10 -15 seconds ahead of your vehicle. 
To avoid last minutes moves, it is important to look down the road 10 -15 seconds ahead of your vehicle so that you can see hazards early enough. Constantly staring at the road just in front of your vehicle is dangerous. As you scan ahead, be alert for vehicles around you. Watch for parked vehicles that are moving into traffic. 

The answer is option a.