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.
These are all examples of a focus group in action. Focus groups are essentially group discussions which rely heavily on the interaction between group members and the relationship between the researcher and the respondents. Focus groups have been a dominant form of qualitative data collection in market research for more than 30 years.