Which of these best describes a scientific variable

A scientific variable is any factor that can be changed or controlled

      The right answer to this question is option C. A factor that may affect an experiment or investigation.

       A scientific variable can be lots of different things, it's up to the experiment and the scientist to decide what is his variable. For example, if I grab a Petri's dish and put bacteria on the right and left side, and then a crescent quantity if antibiotics until the middle of the dish, just to check how these bacterias are going to grow up. In this case, what is my variable? Well, it can be different things, you can assume it's the quantity of antibiotics, bacteria, the size of the dish, thats why it's a variable, you can change it any time you want to fit your experiment.

maybe because its impossible for balloons to lift a whole entire house.

c is the answer to this question. altitude affects the weather because air molecules evaporate.