Biology

Vitamin A deficiency primarily causes night blindness and can also lead to loss of appetite. Therefore, both symptoms listed in options A and B are correct, making option D the best answer.

Hepatitis A is primarily transmitted through the fecal-oral route, often via contaminated water or food. Therefore, water is the correct mode of transmission among the options provided.

Vitamin C is commonly known as Ascorbic Acid, which is essential for the repair of tissues and enzymatic production of certain neurotransmitters. The other options are unrelated substances.

The study of plants is called Botany, which is a branch of Biology. Entomology is the study of insects, and Biology is the broader study of living organisms. Therefore, option A is correct.

A predator is an animal that captures and kills other living animals for food. Parasites live on or in a host and usually do not kill it immediately, scavengers feed on dead animals, and 'None of these' is incorrect here.

Arteries are the blood vessels that carry oxygenated blood away from the heart to the body tissues. Veins carry deoxygenated blood back to the heart, and capillaries are small vessels where exchange of gases occurs.

The color of blood is due to hemoglobin, a protein in red blood cells that binds oxygen and gives blood its red color. Oxygen itself is colorless, and hydrogen is unrelated to blood color.

Vitamin D deficiency leads to rickets, a disease characterized by softening and weakening of bones in children, due to impaired calcium absorption. Measles and scurvy are caused by other factors (measles is a viral infection; scurvy is due to vitamin C deficiency).

The lifespan of white blood cells varies widely depending on the type; some live only a few hours to days, while others can live for months or years. None of the given options accurately reflect this range, so 'None of these' is the correct choice.

Lactic acid is naturally present in milk, primarily due to the activity of lactic acid bacteria that ferment lactose into lactic acid, giving milk and dairy products their characteristic slight acidity. Fresh milk contains lactic acid, although fermented dairy products like yogurt have higher concentrations. In contrast, fresh fruits such as orange and banana do not naturally contain significant amounts of lactic acid, although lactic acid bacteria can be isolated from their surfaces and can produce lactic acid during fermentation processes. Therefore, among the given options, milk is the correct answer where lactic acid is found naturally.