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.
a point at which a decisive change takes place; critical point; crisis. 2. a point at which something changes direction, especially a high or low point on a graph. 3. Surveying. a point temporarily located and marked in order to establish the elevation or position of a surveying instrument at a new station. Origin of turning point.