Remark
The sample was not voluntary. 284 people at random were selected. A is incorrect.
The question was a "yes/no" question. You either supported the motion, or you did not. One response did not influence the other. B is incorrect.
There's no data missing that can't be calculated. 20 people refused to answer for one reason or another. A very large number of people supported the pole so the 20 people would not make a difference no matter how they voted. Still the 20 people were not reported but could be calculated. The better answer is D. <<<< Answer.
You could say C but there are other possible reasons and a more general answer is needed.