Which statement best describes how greenhouse gases act as natural insulators in the earth's system?
a) the gases absorb and emit a part of the heat reflected by earth’s surface.
b) the gases receive the sun’s heat directly and deflect a part of it toward earth’s surface.
c) the gases are formed by the burning of fossil fuels, as a result of which they are very hot.
d) the gases react with each other in the presence of sunlight and release energy in the form of heat.
25)
farmer scott is one of the best farmers in town. during the middle of the corn growing season, farmer scott had to travel out of town for two weeks, and he left his acres of corn plants alone with no chemicals or other protection.

in terms of succession, which of these best describes what framer scott returned to after the two weeks?
a) small weeds began to grow and develop.
b) there was no distinct change in the corn fields.
c) all of the corn died due to a rampant corn disease.
d) the corn mutated to form a new species of vegetable.
26)

lichens, represented by this symbiotic relationship, are responsible for or the establishment of a new site for plant growth.
a) primary succession
b) secondary succession
c) trophic metamorphosis
d) ecological infiltration
27)
which describes an example of ecological succession?
a) a caterpillar developing into a butterfly.
b) a meadow replacing a pond in its flood plain.
c) a climate gradually changing over many eons and becoming colder.
d) the replacement of a native species of animal with an invasive species.
28)
how do beaver dams contribute to species diversity in the ecosystem?
a) provide access to food in winter
b) keep predators away from the ecosystem
c) provide a habitat for a variety of species
d) ensure that only beavers have access to water
29)
volcanoes play an important role in determining climate change. when a volcano erupts it throws out large volumes of gas and ash into the atmosphere which can influence climatic patterns for years.
a) nitrogen
b) oxygen
c) sulfur dioxide
d) carbon dioxide
30)
this is the term for the weather patterns that an area experiences over a long period of time?
a) climate.
b) weather.
c) available energy.
d) position in space.