Imagine that some change in the environment caused boys to start going into puberty at an earlier age than they ever have in the past. which conclusion is most reasonable?

Well if you're given options then I can only answer this question to the best of my knowledge.

So here goes nothing;

If boys are hitting puberty at a younger age and you suspect that its their environment that's causing the issue. First step is to test the environment in which the boys are growing up in to see whats effecting their hormonal imbalances. This can be in the water, air, soil, the house and many other outside influences can cause an early onset for puberty in young boys.