Which of the following heart valves lies between the left atrium and left ventricle and prevents the regurgitation of blood from the ventricle back into the atrium?

Excretion is the process of removing metabolic wastes or excrements from the body.
Metabolic wastes are substances left over from metabolic processes (such as cellular respiration) which cannot be used by the organism and must therefore be excreted.
These include nitrogen compounds, water, CO2, phosphates, sulphates, etc.
Choice B. Absorption is wrong because absorption is the process of taking in substances into the body or cells.
It is not related to the removal of waste.
Choice C. Metabolism is wrong because metabolism is the sum of all the chemical reactions that occur in an organism.
It is not a process of removing wastes, but rather producing them.
Choice D. Assimilation is wrong because assimilation is the process of incorporating substances into the body or cells.
It is also not related to the removal of waste.
Normal ranges for metabolic wastes vary depending on the type and concentration of the waste, as well as the organism and its environment.
For example, ammonia is a very toxic waste that requires a lot of water for its excretion, while uric acid is a less toxic waste that can be concentrated into a small volume.
Some normal ranges for human metabolic wastes are:

Urea: 2.5 to 6.4 mmol/L in blood serum Uric acid: 3.4 to 7.2 mg/dL in blood serum Creatinine: 0.6 to 1.2 mg/dL in blood serum CO2: 35 to 45 mmHg in arterial blood gas

Persons with type AB blood are sometimes called universal recipients, not donors. This means they can safely receive a blood transfusion using any other blood type. Choice A is wrong because it confuses type AB blood with type O negative blood.

Type O negative blood is considered the universal donor type because it has no antigens on the surface of red blood cells and can be given to people of any blood type.

Type AB-positive blood is also considered the universal plasma donor type because it has both A and B antigens and can be given to patients with any blood type.

Plasma is the liquid part of blood that carries cells and proteins throughout the body.

The presence or absence of antigens and the Rh factor determine how a person’s immune system reacts to a blood transfusion or organ transplant.

Antigens are substances that can trigger an immune response if they are foreign to the body.

The Rh factor is a protein that can be either present (+) or absent (-) on the surface of red blood cells.