User: The greenhouse effect is a result of A. absorption and radiation of energy in the hydrosphere. B. consumption of fruits and vegetables that produce a biofuel. C. absorption and radiation of energy in the atmosphere.
A principal focus or focal point is a special focus: 1  For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal pointsâone on each side.
focus noun [ C ] (CENTRE) C1 the main or central point of something, especially of attention or interest: I think Dave likes to be the focus of attention. The main focus of interest at the fashion show was Christian Lacroix's outrageous evening wear.