Which of the following statements best supports the hypothesis that viruses can cause cancer?

The number of protons in an atom is equal to its atomic number. In this case, lithium has an atomic number of 3, so it contains 3 protons.

The other choices (A, C, and D) do not represent the correct number of protons for a lithium atom.

The nervous system is divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, while the PNS consists of all the nerves outside of the CNS.

The pulmonary vein is the only vessel in the list that carries oxygenated blood. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it gets oxygenated. The superior and inferior vena cava are large veins that carry deoxygenated blood from the upper and lower body, respectively, to the heart.

The answer lies in the environmental conditions of the Alps. The body was quickly frozen by the low temperature and covered by snow and ice, which prevented exposure to air, moisture, and microorganisms. The freezing also slowed down the chemical reactions that would normally break down the body's cells and tissues. Thus, the body was preserved in a natural mummy state until it was discovered by modern humans.

Reverse transcriptase, an enzyme encoded by the virus. This enzyme can convert the viral RNA into DNA, which can then integrate into the host cell's genome and hijack its machinery to produce more viruses. The other options are not relevant to this process. Receptor proteins are involved in binding the virus to the cell membrane, but they do not insert viral DNA into the cell. The phospholipids and the protein capsid are structural components of the virus, but they do not have any enzymatic activity.

To produce only offspring with smooth leaves, the parents must both have two copies of the recessive allele (f) for this trait.

Cytokines are small proteins that act as chemical messengers between different types of immune cells. They can stimulate or inhibit the activation, proliferation, differentiation, and migration of immune cells. For example, interleukins are a type of cytokine that is produced by one type of white blood cell and can affect the behavior of another type of white blood cell. Lysozymes, perforin, and granzymes are all molecules that are involved in killing pathogens or infected cells, but they do not directly activate other immune cells.

One of the functions of the skin is to protect the body from harmful effects of ultraviolet (UV) radiation. UV rays can damage the DNA of skin cells and cause mutations that may lead to skin cancer. The skin has a natural defense mechanism against UV radiation, which is the production of a pigment called melanin. Melanin is synthesized by specialized cells called melanocytes, which are located in the basal layer of the epidermis. Melanin absorbs UV rays and prevents them from reaching the deeper layers of the skin.

The pancreas releases sodium bicarbonate into the duodenum, the first part of the small intestine. The main function of sodium bicarbonate is to neutralize the acidity of chyme, the semi-digested food that comes from the stomach. By doing so, sodium bicarbonate creates a more alkaline environment that is suitable for the action of pancreatic enzymes. Sodium bicarbonate does not affect peristalsis, the rhythmic contraction of the intestinal muscles, nor does it stimulate the pyloric sphincter, the valve that controls the passage of food from the stomach to the duodenum. Sodium bicarbonate is not a protease, an enzyme that digests proteins, nor does it digest carbohydrates.

Erythropoietin is a hormone that is produced by the kidneys and stimulates the production of red blood cells in the bone marrow. Red blood cells contain hemoglobin, a protein that binds to oxygen and transports it to the tissues. Therefore, erythropoietin helps to maintain adequate oxygen levels in the blood and prevent anemia.