Explain how the following 4 words are connected: Gene, Allele, Genotype,
Phenotype?

Different forms of a gene are called alleles.The alleles an individual has at a locus is called a genotype. The genotype of an organism is often expressed using letters. The visible expression of the genotype is called an organism's phenotype.

(not 100% sure)

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

this is a good question! i'll do some research and come back when i have the answer!