The independent variable is the only factor that a scientist

So we want to know what does a scientist do with the independent variable. In the procedure known as control of variables we have dependent, independent and controled variables. The independent variable is the one variable which is being changed by the scientist while the others are kept constant. So the correct answer is "changes".

Julia would be observing a. static electricity was caused by her sweater rubbing against her shirt and transferring electrons. she didn't touch anything metal, so that would cancel out b.she most likely didn't rub her sweater against her hair either, so that cancels out c.she also didn't scoot across the carpet while trying to take her sweater off, that cancels out d.so that leaves a.a. is correct.