Manoj1998
egmat GMATNinjain option D, Is using "for verbing" correct because astronomers have developed it for a purpose shouldn't we use "to-verb " here?
I'd be very careful about trying to establish a general rule here. Consider some simple examples:
1) Tim painted mustaches on his children's Frozen dolls to teach his kids a lesson.
Here, "to teach" gives us information about the main verb of the clause, telling us
why Tim painted mustaches on Disney princesses.
2) Tim punished his kids for violating curfew.
Now, "for violating" also gives us information about the main verb of the sentence, telling us why Tim punished his kids.
3) Tim bought a device for measuring the size of his children's cranium.
In this case, "for measuring," seems to describe "the device," giving us information about
what kind of device.
4) Tim bought a device to measure the size of his children's cranium.
Now "to measure" seems to tell tell us why Tim bought a device, but I suppose you could also argue that it's describing what the device is used for.
The point is that these modifiers appear to be fairly versatile, and their meaning is determined more by context than by any strict usage rule.
Put another way, I wouldn't use "to" vs "for" as a viable decision point, at least not in isolation. Instead, as others have pointed out, I'd see that "to rate how likely a particular asteroid or comet will be" doesn't make sense. They're not rating how likely it is for a comet to
be, or exist; they're rating the likelihood that the comet will collide with Earth. That's enough to remove (C), without agonizing over whether "to" or "for" is better here.
I hope that helps!