Answer
The independent variable is Reduced air pressure, the dependent variable is behavioural tests and control variable is the strain of the rat
Step-by-step explanation
In this question, the air pressure is going to reduce upon the rats to observe its effects on pregnant rats. So the reduced air pressure will be an independent variable which cannot be control in the environment but the behaviour of the rats changes with changing environmental conditions such as reduce pressure. So the behaviour change is the dependent variable. The strain of the rate can be changed by the researcher as changing present condition can be observed on any specific strain of rats.