The correct answer is option 4: All options are correct. All of the options mentioned - physical contact, vectors, and water - can act as agents of infection.

Physical contact refers to direct interaction between individuals, which can facilitate the transmission of pathogens from one person to another. This can include activities such as shaking hands, hugging, or sexual contact.

Vectors are organisms, such as mosquitoes or ticks, that can carry and transmit disease-causing pathogens. When a vector bites a person, it can transfer the pathogen into their bloodstream, leading to infection.

Water can also serve as a source of infection if it is contaminated with disease-causing microorganisms. Consuming or coming into contact with contaminated water can introduce pathogens into the body and lead to infection.

Therefore, all three options - physical contact, vectors, and water - have the potential to act as agents of infection.