The distance from airport or seaport which has to be free from mosquitoes is-
**Core Concept**
The concept being tested here involves **vector control** and **public health measures** to prevent the spread of diseases transmitted by mosquitoes, such as malaria, dengue, and yellow fever, near international portals of entry like airports and seaports.
**Why the Correct Answer is Right**
To prevent the introduction and spread of mosquito-borne diseases, it is crucial to maintain a certain distance around airports and seaports that is free from mosquitoes. This distance is typically considered to be 400 yards, as mosquitoes generally do not travel far from their breeding sites, and this radius can help in significantly reducing the risk of disease transmission.
**Why Each Wrong Option is Incorrect**
**Option A:** This distance is too short to effectively prevent mosquito-borne disease transmission.
**Option B:** While a larger radius might provide additional protection, 400 yards is the standard distance considered effective for mosquito control around ports.
**Option D:** This option is not relevant to the standard public health guidelines for mosquito control around airports and seaports.
**Clinical Pearl / High-Yield Fact**
Remember, mosquito control is a critical aspect of preventing the spread of infectious diseases globally, especially around points of international travel. The distance of 400 yards is a key figure in public health policy for airports and seaports.
**Correct Answer:** C. 400 yards.