GMAT Critical Reasoning (CR) | Participants at a continuing legal education seminar were asked

In A 85% returned - majority means more than 50% . so we get that out of all 100% people participating . around 43 % accepted to change. We don't know about rest . 15% of people.
It does't give adequate information to say that it strengthens.

Can you explain me What C is actually intending to say.
To my bad, I eliminated all options.

C states that - percentage of people who wanted schedule = Percentage of people who returned . ? what if only 10 % returned
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