Which form in the following sentence is correct? " For+ verb+ing " or " to + infinitive"

Hello there,

The following sentence is one of the questions of GMAT that I put here:

Responding to the public's fascination with-and sometimes undue alarm over-possible threats from asteroids, a scale developed by astronomers rates the likelihood that a particular asteroid or comet may collide with Earth.

A. a scale developed by astronomers rates the likelihood that a particular asteroid or comet may
B. a scale that astronomers have developed rates how likely it is for a particular asteroid or comet to
C. astronomers have developed a scale to rate how likely a particular asteroid or comet will be to
D. astronomers have developed a scale for rating the likelihood that a particular asteroid or comet will
E. astronomers have developed a scale that rates the likelihood of a particular asteroid or comet that may.

According to official stuff, the answer is 'D'. Although from the sentence the intention can be easily understood, the answer states that the Scale was not the intention! What do think, and how do you prove that the sentence does not state any intentions for developing the scale?
Moreover, is it correct to say this sentence: " Many methods have been proposed to estimate the variations of Tectonic Plates annually", or "Many methods have been proposed for estimating the variations of Tectonic Plates annually" .

Thank you