Question

these investigations are observational studies. pick a valid criticism of investigations c and d. they both lack a control group. neither study uses enough wind meters. they both interfere with a study in progress. neither study allows time for testing wind variation.

Explanation:

In observational studies, having a control group is crucial for comparison and to draw valid conclusions. Without a control group, it's difficult to determine if the observed effects are due to the variables being studied or other factors. The other options about wind meters, interfering with a study in - progress, and testing wind variation are not as fundamental criticisms as the lack of a control group for observational studies.

Answer:

They both lack a control group.