A looks like it’s pointing towards the nucleus, but since that’s not an option, we can assume it’s pointing at what’s surrounding the nucleus, which is the cell body.
C is an axon.
D is an axon terminal, so named because when neurons form a chain, they attach at their ends, so “terminal” makes sense.
Human being plays a key role to maintain ecological balance because they have the highest thinking capacity as compared to other living organisms. Sufficient food availability to all living organisms and their stability reflect the existence of ecological balance.
A sex-linked trait is a trait that is carried by the X chromosomes in females but it is not expressed(the phenotype). Females are only carriers because they have two copies of the X chromosome [one of them carries the trait and the other does not]. Males who inherit one copy of the X chromosome often get the trait (because the trait is in either one copy or the other of the X chromosome) and express it while their Y chromosome would became recessive. Thus, only males express sex-linked traits such as hemophilia or color blindness