The drug was tested on a group of 50,000 elderly patients who had cancer. The tumors in most of the patients did not respond to the treatment.

The scientists concluded that the drug was not effective in fighting cancer.

What is the most important problem with the design of this investigation?

the sample size is too small to be valid

The bottom one.

The sample size is too small to be valid

Explanation:

Since the question is asking for a nonscientific question you want to rule out answers that would be reasonable to ask that has something to do about the birds.

Think of the questions as a experiment. D. Would the birds still visit if the seed in the feeders were changed. That would be a very good scientific explanation. So D. is wrong.

C.At what time of day do the most birds visit the feeders. That would be a fun scientific experiment wouldn't it? That rules C out.

Now you have A. and B left. B. Does having a birdbath present affect the feeding habits of the birds? That would be another good experiment.  Your answer is A. What color are the beaks of the small birds that visit the feeders?

I hope that helps! If it does please mark me brainiest, if it doesn't please don't.