Which of these can make the vehicle skid?

A skid happens whenever the tires lose their grip on the road. This is caused in one of four ways:
Over-braking. Braking too hard and locking up the wheels. Skids also can occur when using the speed retarder when the road is slippery.
Over-steering. Turning the wheels more sharply than the vehicle can turn.
Over-acceleration. Supplying too much power to the drive wheels, causing them to spin.
Driving Too Fast. Most serious skids result from driving too fast for road conditions. Drivers who adjust their driving to conditions don’t over-accelerate and don’t have to overbrake or over-steer from too much speed. [Commercial Driver License Manual]