D. Spiting when exited or upset.
A, B, and C are all physical traits that have nothing to do with emotions.
<u>Answer:</u>
The correct answer option is: frequency of the recessive allele.
<u>Explanation:</u>
When there are no mutations, no selective forces, no gene flow, no non-random mating and large population size, the population is said to be in Hardy- Weinberg equilibrium.
When Hardy-Weinberg equilibrium is met, it is written in the form of an equation which is as follows:
where 
represents the frequency of the homozygous dominant allele, 
is the frequency of the heterozygous allele while q or
represents the frequency of the homozygous recessive allele.
The limbic system is a region in the brain consisting of the thalamus, the hypothalamus, the hippocampus, and the amygdala.
When a person has amygdala damage, it would be expected to disrupt the integration of fear.
So, this kind of person will be efficient under fear situations avoiding emotional burnout.
Careers like bridge climbing or skydiving instructor are good for this kind of person.
The best answer is B - Proteins.
Proteins make up enzymes, or to put it another way enzymes are made up of protein. It is enzymes that speed up the chemical reactions. Enzymes are organic catalysts, substances that speed up a (biochemical) reaction but do not take part in the reaction and remain unchanged at the end of the reaction.
In man, there are many enzymes. The majority of these are found in the digestive system where they greatly aid the process of food breakdown from complex molecules to simple molecules. Examples include salivary amylase found in saliva, which begins the gradual breaking down of starch into glucose right from the moment food is placed in the mouth and mixed with saliva. Pepsin in the stomach breaks down protein.
