Of 200 people surveyed, 120 own a car, 80 own a bicycle, and 30 own both. If a person who owns a bicycle is selected at random, what is…

This is a conditional probability. The person owns a bicycle, so the sample space is the $80$ bicycle owners, not all $200$ people. Of these, $30$ also own a car. The probability is $\frac{30}{80}=\frac{3}{8}$, choice C. Choice A ($\frac{30}{200}$) divides by everyone surveyed, which gives the probability of owning both. Choice B ($\frac{30}{120}$) divides by the car owners, which answers the reverse question. Choice D ($\frac{80}{200}$) is the probability of owning a bicycle at all. Always identify the condition and use it as the denominator.