At the earth's surface, warm air expands and rises, leaving behind what is known as an area of ; cold air is dense and sinks to the surface to create what is known as an area of

your choices are, convention, conduction, low pressure, and high pressure

Low-pressure zone

High-pressure zone

Explanation:

When the surface of the earth is heated due to the heat energy radiated from the sun, the air mass near the earth's surface also gets heated up, as a result of which it becomes warm and less dense and eventually rises up. This warm air when rises upwards, forms a low-pressure zone, which subsequently results in the occurrence of rainfall.  Here, the atmospheric pressure remains lower than that of nearby areas.

Again, When the warm air rises up, it experiences lower temperatures and cools down. As it cools, it again becomes dense and thereby falls back, forming a high-pressure zone, where the atmospheric pressure remains relatively higher than the surrounding places.

this allows people to make the best decision or pursue the best option. when alternatives are weighed using their advantages and disadvantages, the option whose disadvantages outweigh the advantages (based on a qualitative or quantitative analysis) are shunned while those whose advantages outweigh their disadvantages are pursued.  

c)as speed changes, wavelength and frequency change.

everything changes!