Here, given-
homozygous alleles 'a' have a frequency of 0.3.
Also the alleles are in equilibrium in a Hardy-Weinberg population. The frequency of individuals that are homozygous for this allele are= 0.49.
The Hardy-Weinberg equilibrium can be defined as the principle which states that the variation in the genetic makeup of a population remains constant and unchanged till there are no external interferences, influencing the population.
Calculation-
Then to find the frequency of the individuals homozygous for this allele the following formula needs to be used-
Thus, the individuals homozygous for the allele can be calculated by 
Learn more about the Hardy-Weinberg equilibrium here-
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The answer is B since climate change is already a huge issue in today’s society
Sunlight is the original source of almost all energy in most ecosystem.
Available oxygen
Available oxygen is the amount of oxygen present at a specific time that can be used in aerobic cellular respiration.
Aerobic cellular respiration is a metabolic process that occurs within the cells of organisms. In this process, oxygen is used in the mitochondria to chemically convert organic molecules such as glucose into adenosine triphosphate (ATP), with the release of water and carbon dioxide as waste products. Aerobic cellular respiration results in a larger amount of energy (ATP) which is used by the cell to perform its activities.
