The argument is that “our health is at much greater risk from natural pesticides than from synthetic ones.”
A – Wrong
This actually strengthens the argument as it says natural pesticides can harm animals (humans are also animals).
B – Correct
This weakens that argument. If humans have become tolerant of such natural pesticides, then they cannot harm us, meaning our health will not be at greater risk.
C – Wrong
This again strengthens the argument. The last line suggests that we consume a vast amount of natural pesticides compared to synthetic ones. C states that natural pesticides can be harmful.
D – Wrong
This is not relevant for the argument which states natural pesticides can harm us.