Explanation:

Let’s break it down:

- The sentence is: "Science has discovered and invented many things to _____ pain and cure terrible diseases."

- Aggravate pain means to make pain worse. Science isn’t usually about making pain worse here.

- Alleviate pain means to make pain less or reduce it. That fits perfectly: science aims to relieve pain and cure diseases.

- Nurture pain is odd—“nurturing” refers to helping something grow, which doesn’t make sense for pain.

- Intensity pain isn’t right. You might *intensify* pain, but that’s the opposite of what this sentence is going for.

So, the right word here is *alleviate*. It matches the context of science improving lives by reducing suffering.