Answer: Phenotype
Explanation:
The phenotype is the set of physical characteristics of an individual, that make it different from other individuals and are evident to the eye.
While the genes inherited from the parents determine the genotype of the individual, that's not enough to fully determine how it will look when it develops, as the ambient where it will grow takes a great part of it. Those factors are called epigenetics.
How an individual will look, its phenotype, is a result of its genes and the epigenetic factors.
The walls of veins are thinner than arteries The blood pressure in veins is less than that in arteries.
Excitation-contraction coupling refers to the series of events that begins with the excitation of the sarcolemma in response to stimulation by a neurotransmitter, and results in the release of calcium ions from the sarcoplasmic reticulum.
Hence, option D is the 1st process that starts the excitation-contraction coupling.
The answer is concentration gradient. Have a good day.
