Many plants and animals would die off <span>if a nearby volcano erupted and filled the sky with dust particles, which caused significantly less sunlight to reach the ecosystem over the course of a year.</span>
The control group is the part of an experiment that does not receive the variable and is used for comparison.
'Red shift' is a key concept for astronomers. The term can be understood literally - the wavelength of the light is stretched, so the light is seen as 'shifted' towards the red part of the spectrum.
Hope this helps.