Ideally, a hydrogen fuel-cell vehicle has no environmental impact. Energy is produced by combining hydrogen with oxygen pulled from the atmosphere, and the tailpipe emission is water. The hydrogen fuel could come from a number of sources (Iceland recently started pulling it out of the ground).
4) Fast, Slow and Long Shutter Speeds. Fast shutter speed is typically whatever it takes to freeze action. For me, it is typically above 1/500th of a second for general photography and above 1/1000th of a second for bird photography. NIKON D700 @ 420mm, ISO 450, 1/2000, f/5.6.
The rule of thumb When I started in photography the rule of thumb was really simple. When hand holding your camera the shutter speed should match or exceed the lens focal length. In other words if you wanted a sharp, shake free shot with a 50mm lens your shutter speed would be 1/50 th sec or faster. Whilst that was fine in its day the world has moved on and so has my rule.