There are two arguments taking place in this stimulus, and our goal is to identify how one arguer, Jay, interprets the other, Helena. To do that, we should first make sure we fully understand both arguments. If we don't understand what's going on, it will be difficult to describe what Jay is responding to.

Let's start with Helena's argument. Helena concludes that how sociable someone is isn't "biologically determined." This is because children born to introverts but raised by extroverts are less introverted than children both born to and raised by introverted parents. What Helena's getting at is that how someone is raised can affect their level of sociability. This is what she means by "not biologically determined": that biological factors are not the only influence over sociability.

Now let's consider Jay's argument. Jay's conclusion is simply that Helena is wrong, but why? Because some children born to introverts but raised by extroverts stay introverted. The thing is, this doesn't counter Helena's argument as we understand it. If Helena is simply saying that how children are raised can also influence their sociability, the fact that it's not the only influence doesn't disprove her conclusion. So for Jay to think that that evidence rebuts Helena's argument, Jay must think that Helena is arguing biology plays no role at all.

In short, the issue here is that there are two possible interpretations of "not biologically determined". One interpretation is "not exclusively determined by biology", and the other is "not determined by biology at all". It seems that Jay subscribes to the second interpretation, so that's what we're looking for in the answer choices.