If “eco-friendly” detergents contain much lower amounts of environmentally damaging surfactants than other detergents, this gives a reason to believe that they might be less damaging to the environment, even though the effects of most of their ingredients are unknown.

The columnist’s argument is about the environmental effects of those detergents that are advertised as eco-friendly. Whether or not there is reason to believe that regular laundry detergents harm the environment doesn’t weaken her conclusion about “eco-friendly” detergents.

This is too vague to weaken the columnist’s conclusion because we don’t know which kinds of detergents contain which kinds of surfactants. Do “eco-friendly” detergents contain more harmful or less harmful surfactants? (C) doesn’t give us this information.

Like (C), this is too vague to impact the columnist’s argument. We don’t know which detergents contain these other, more harmful ingredients, so we can’t conclude anything about the effects of “eco-friendly” detergents.

If larger amounts of “eco-friendly” detergents must be used and these detergents contain harmful surfactants, (E) strengthens the columnist’s conclusion that there is no reason to believe that “eco-friendly” detergents are less damaging to the environment than other detergents.