The answer would be d) phenotype. The phenotype is the physical characteristic while the genotype is the combination of alleles from the parent--basically the part that you can't really see. The color of a flower is prominent, so that would be its phenotype. An organism's phenotype can also include certain behavioral characteristics as well, not just the way it looks! Hope this helped :)
The answer is B. Bacteria blooms and decreased underwater photosynthesis causes asphyxia, killing the fish.
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The brain's suprachiasmatic nucleus regulates the body's circadian rhythms. The suprachiasmatic nucleus is a minute region of the brain located in the hypothalamus above the optic chiasm, the circadian rhythm is the 24-hour cycle of organisms, related to sunlight and temperature.