How to deal with analyzing optional survey data
Your best bet is to change the way you ask question C and the way you measure it. Giving a yes / no response for C will not let you gauge the actual spiciness so you need to adjust it to a scale and allow individuals to rank it. While all of your questions are fairly subjective, C is the most so as tolerance to spice plays a big role in if one thinks it spicy or not.

I suggest using a 1-5 scale, as you have for the others, and give comparative suggestions for each level of the scale e.g. 1 is eating bread while 5 is equivalent to eating a habnero pepper.