Option (e) Partly form ERG signal is the only correct statement.
You might've known the basics of Retina.
Cones are sensitive to colors, while rods respond mostly in dimming light.
Now let's analyze each of the choices.
(a) Cones are dense in Fovea, not the rods!
(b) Cones are specialized for color sensation.
(c) Rods don't even respond to colors, let alone red color.
(d) Again cones make fine details, but rods just make a fade image in the dim light.
(e) ERG stands for Electroretinography . In this test, both your rods and cones are tested.
In relatively fade and dim ERG light signal , rods are sensitive.
So, first four choices aren't true for rods, and the best choice is Option (e)!
For further queries, confusions, ask in the Comments.