If we design two scribbling machines$*,$ one with a $4-$battery case and long markers, and the other with a $2-$battery case and short markers, then the scribbling machine with the $2-$battery case will move faster than the other machine because the short markers will make the machine less wobbly.

$"$We tinkered with these machines in class.

We can say that:

The investigation includes a fair test.

The hypothesis includes more than one dependent variable.

The hypothesis is testable

The hypothesis includes more than one independent variable