Which pair of statements best describes an essential amino acid?

What causes darkening of the skin as melanin production increases

The nervous system interacts with the endocrine system by a. using hormones as connections b. sending nerve impulses directly to glands c. using neuroendocrine cells as connections d. sending neurotransmitters directly to neurons

In 2001, records showed that local stocks of fish were down worldwide. yet, records of harvests indicated that fish were being taken at records rates. what was actually happening?