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.
ISO is how sensitive your camera is to light, shutter speed is how long it takes for your camera to take a picture (which in turn alters the amount of light coming in), and aperture is how dilated the lens of your camera is. Not all cameras have this, mostly only digital photography cameras.