Vectors can be defined asAnimals carry the infecting agents from sick person to another healthy personMicroorganisms which cause many diseasesInfected personDiseased plants

In the context of biology and disease transmission, vectors are organisms that do not cause disease themselves but spread infection by conveying pathogens from one host to another. This term is commonly used in the field of epidemiology.

For example, mosquitoes are a vector for malaria. They carry the malaria parasite from one person to another during their feeding process. Similarly, ticks can be vectors for Lyme disease.

So, in the options you provided:

1. "Animals carry the infecting agents from sick person to another healthy person" - This could be considered a vector if the animal is carrying a pathogen from one person to another.

2. "Microorganisms which cause many diseases" - This is not necessarily a vector. While microorganisms like bacteria and viruses can cause diseases, they are not vectors unless they are carried by another organism to a new host.

3. "Infected person" - An infected person can be a source of disease for others, but they are not considered a vector. The term vector is usually reserved for organisms that carry disease from one host to another.

4. "Diseased plants" - Similar to the infected person, diseased plants can be a source of disease, especially for other plants, but they are not typically referred to as vectors. However, insects that spread disease from one plant to another would be considered vectors.

In the context of biology and disease transmission, vectors are organisms that can carry and transmit infectious pathogens into other living organisms. These vectors are typically blood-sucking insects which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later inject it into a new host during their subsequent blood meal. So, in your list, the first option is the correct definition of vectors.