Exposure to sunlight helps a person improve his health because
Options: the infrared light kills bacteria in the body, resistance power increases, the pigment cells in the skin get stimulated and produce a healthy tan, the ultraviolet rays convert skin oil into Vitamin D
Benjamin Franklin was a prolific inventor. He invented the lightning rod, the Franklin stove, studied electricity, discovered the Gulf Stream, started the first library, and on and on. Among his many other inventions, what musical instrument did he invent?
On a night when the sky is clear, the temperature may dip considerably; on a cloudy night the temperature will usually dip much less. The reason for this difference is that
Options: the clear sky allows radiant energy to escape readily from the earth, on a cloudy night the clouds are warm and therefore retard the cooling, the clear sky allows the cold of outer space to reach the earth, current of air carry the heat away from the earth on a clear night
The periodic rise and fall of the sea level on the earth, gives rise to tides. This is related to
Options: the position of the moon with reference to the earth and the gravitational pull exerted mainly by the moon and partly by the sun, infrared rays from the sun, ultraviolet rays from the sun, None of the above
Options: whenever the normal decrease of atmospheric temperature, when the decrease in temperature or moisture or both takes place, whenever the normal decrease of atmospheric temperature or moisture or both change with height over a short vertical interval, All of the above