Agel electrophoresis is performed, but when the gel imager is used, no bands appear. the researcher might have forgotten to: (check all that apply):

The answer is;

a. add electric current.
b.add buffer solution

The process of gel electrophoresis taps on the property of net charges of molecules to ensure that they travel up the gel. Additionally, the buffer acts as the mobile phase for the molecules and also give molecules net charge as they travel through the gel. It is until the molecules reaches an isoelectric point,where the molecule has zero net charge, that they stops moving through the gel. This is how bands are formed.

It's speed of rotation.