Answer:
C/ a controlled lab experiment with mosquitoes that limits water access for the experimental group.
Explanation:
The scientist is looking for what could cause the decline in the mosquito population and if it is due to the filling of the local pond. To best conduct research on this topic would be to experiment with mosquitoes and their responses with limited water access. It has the two variables, the mosquitoes and water. This is the most effective way of determining his study.