Answer:
The answer is "d" endogenous factors
Step-by-step explanation:
Endogenous factors or internal factors control and influence the internal environment. They are internal factors that make up the characteristics of a place. During experiment or trials, the endogenous factors are tweaked to provide the condition needed for such an experiment, this is usually done in a confined or enclosed space.
The car companies build these wind tunnels to get control of these endogenous factors in the wind tunnel. These variables that can be controlled and altered in the wind tunnel is referred to as endogenous factors