ya, option (b) definitely doesn't work.

"greater than..." can only be used to compare two kinds of things:
1/ NOUNS representing things that can be compared quantitatively;
2/ actions formed from "to be" or from similar verbs, such as "to seem ADJ", "to appear ADJ", and so on -- basically, the kind of verbs that say what someone or something is, not what he/she/it does.

so, "greater than..." can compare two amounts.
also, although this doesn't happen in the problem at hand, it can compare item #2 above: my body fat percentage is 2% greater than it was last year.

"greater than..." cannot be used to compare action verbs, such as "raised".
so, your instinct is closer to the mark than the OA here.

in fact, now that i think about it, and this is not even a special property of "greater than...". instead, it just flows from the fact that "great(er)" is an adjective. in other words, the restrictions in my post above hold for pretty much all constructions of the type "ADJ-er than..."

as an illustration, let's take a random adjective, say, "quick".
* comparing nouns: i am quicker than my little brother.
* comparing "to be" (or equivalent) verbs: i'm quicker than i was five years ago.

there you go.
note that this isn't a new concept: these are precisely the same kinds of things that can be modified by normal (non-comparative) adjectives.
* nouns: this is a difficult problem.
* nouns with the types of verbs described above: this problem seems difficult.
etc.

iongmat wrote:Why can't B be interpreted as:

..an amount greater than (amount) any other candidate raised.

comparisons must explicitly compare a pair of parallel things. there's some flexibility there, but, if you get rid of the parallel things, you don't have a valid comparison anymore.

e.g.
more people take taxis to the airport than drive to it
here, "take taxis to the airport" is parallel to "drive to it".

more people take taxis to the airport than from it
here, "to it" is parallel to "from it".
you could argue about whether there's an omission of "take them" from the latter part, but there's still actually a parallel structure there.

if you have "an amount greater than X raised", then nothing at all on the right-hand side is parallel to "an amount". no go.