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.
4. the source of an influence, action, or force: the center of a problem. 5. a focus of interest or concern. 6. a principal point, place, or object: a shipping center. 7. a building or part of a building used as a meeting place or having facilities for activities. 8. an office or other facility providing a service or dealing with a particular emergency. 9. a person, thing, or group occupying the middle position, esp. a body of troops.