Because a stationary front marks the boundary between two air masses, there are often differences in air temperature and wind on opposite sides of it. The weather is often cloudy along a stationary front and rain or snow often falls, especially if the front is in an area of low atmospheric pressure.
C. Solar energy's whole purpose it to reduce pollution in the air that fossil feuls do not. The answer cannot be A. B. or D. because 1. it is expensive 2. it can only be used during the daytime. It is a SOLAR panel. and 3. like is said earlier it is not free.