Vector insects are which
A. Spread disease
B. Destroy crop
C. Spoil soil
D. Act as scavengers

Hint: A vector insect is a living organism that transmits an infectious agent from an infected animal to a human or to the other animal. Biological vectors, such as mosquitoes and ticks may carry pathogens that can multiply within their bodies and be delivered to new hosts, usually through biting.

Complete answer: The insects that transmit disease are called the vector and the disease is mentioned as a vector disease. The insects act as mechanical vectors which means that they can carry an organism, but the insect is not essential to the life cycle of the organism. For example, a housefly carries organisms on the outside of their bodies that causes diarrhoea in people. Insects also serve as the obligatory hosts where the disease-causing organism must undergo development before being transmitted. The vector-borne transmission of the disease can take place when the parasite enters the host through the saliva of the insect during a blood meal or from the parasites inside the feces of the insect that defecates immediately after the blood meal. The parasites transmitted by the insects are circulating in the blood of the host, with the parasite residing in and damaging the organs or other parts of the body. Hence the vector insects are those who spread diseases.
Therefore, the correct answer is option A.

Note: Some of the disease vectors are as follows:
-Malaria: The Anopheles species of the mosquito.
-Lymphatic filariasis: Culex, Anopheles, Aedes species of the mosquito.
-Dengue: Aedes species of the mosquito.
-Leishmaniasis: Phlebotomus species of the sandfly.