Many Studies Have Been Conducted on the Effects of Having

Multiple Choice

Many studies have been conducted on the effects of having a pet on the response to medical problems and on mental health. But doctors in Berlin were interested in the effects of having a pet bird on lung cancer. (I assume they were wondering if birds might cause air pollution that could lead to lung cancer.) They asked 239 patients with lung cancer and 429 controls without lung cancer whether they had a pet bird. Ninety eight of the 239 patients did have a bird, while 101 of the 429 controls had a bird. (That strikes me as a very high percentage of bird owners, but those are the data.)
How might this study be "improved" as a conclusive test of the hypothesis that birds cause cancer?

A) People should be randomly assigned to having a bird or not having a bird.
B) People should be randomly assigned to the lung cancer group.
C) The sample size should be greatly increased.
D) None of these would help the situation.