Sentence Correction

794. The Olympic Games helped to keep peace among the pugnacious states of the Greek world in that a sacred truce was proclaimed during the festival’s month.
(A) world in that a sacred truce was proclaimed during the festival’s month
(B) world, proclaiming a sacred truce during the festival’s month
(C) world when they proclaimed a sacred truce for the festival month
(D) world, for a sacred truce was proclaimed during the month of the festival
(E) world by proclamation of a sacred truce that was for the month of the festival

Hi,
The answer is C but why B is wrong?

E is wordy and awkward....I feel C is wrong because it uses the word "when" which makes the event sound like a single event rather than a continuos trend....A (in that a sacred....seems awkward....Is it B? I am not too sure though

Yes...My guess was B as well, but official answer is C.

Can anyone explain why B is wrong??

The answer seems to be C