@vivianacostante fellow E picker here. I don't know if you had the same issue, but on my first read, I misunderstood the timeline as:

1980: rare amount of birds

1980 - 1999: rare amount of birds

2000: suddenly a lot of birds

Under this perspective of events, it would make sense to pick E. Predators were hunting birds until the year 2000, and so when they were gone, the bird population grew. However this is the wrong interpretation of the timeline. You can tell by the wording: "was rare in Nova Scotia in 1980;[...] By 2000 [...] were quite common" which does imply a continuous increase of the population. So the timeline actually looks like this:

1980: rare amount of birds

1980 - 1999: increase in the amount of birds

2000: large amount of birds

Now E doesn't work at all as the existence of predators clearly didn't affect the bird population. Now A does make sense, as the bird feeders keep attracting more and more birds. Hope that helps in some way

I think this question is hard because it fights our "common sense". We would think that to weaken the argument, we have to fight the biggest assumption: that other ingredients could also harm the environment. And the remote possibility of harming the environment seems like a bad thing on its own. BUT just from the info given, and NOTHING ELSE, we do know that: 1. surfactants harm the environment, and 2. we do not know what the other ingredients do. with this limited knowledge, less surfactants do represent a benefit, because there is a chance that the other ingredients do... nothing!

the conclusion of the arg is "there is no reason to believe eco detergents are less damaging", but there could be a reason, that, all things equal, one of them has less "poison" than the other.

You can see it in a different case like, say you are on a diet and are trying to eat more healthy. You are given 2 meal options. You do not know the nutritional information of either, but you get the calorie amount. The lower calorie food could be a better pick, even if you are unaware of the ingredients. The arg is saying there is no way to know, but there is one comparable element.

Hope this helps!