Please help: A specific MC question that puzzles me

Test Preparation SAT Preparation
1

<p>Please identify an error in the following sentence:
The first signs in six months of a pickup in consumer spending (A)<em>are emerging</em>, (B)<em>which reduces</em> the chances (C)<em>that</em> the Federal Reserve will lower interest rates when (D)<em>it meets</em> next month. </p>

<p>The answer is B, but I cannot accept the explaination. " The error in this sentence occurs at (B), where the participial "reducing" should appear, but the relative phrase "which reduces" appears instead. "</p>

<p>As far as I know, participal and relative clauses led by "which" are, most of the time, interchangeable.</p>

<p>I chose C, because I have a little problem with the match of "that" and "chances". I prefer something like "...reduces the chances + prep. (by?)+ which the Federal Reserve will...."</p>

<p>If you would explain why the answer is B, please help.
Thanks in advance :)</p>

2

<p>It's choice B, reduces should be reduce to complement SIGNS.</p>

3

<p>Thanks simple1. I was thinking maybe "which" is referring to the whole main clause instead of "signs" so that it takes a singular verb, but your explaination is the best so far to the choice B.
Thank you!^-^</p>