Answer:
A cross sectional study
Explanation:
The cross-sectional study refers to the observational study which involves the sampling or collection of data from the individuals of various age.
The study is performed to study wither one or more than one variable at a single point of time by the economist and the biologists to study the behaviour of the person and the differences related to that. The study is usually non-experimental but is a descriptive study.
In the question, since the Dr. studies, the variable ice cream preference for different age groups at a single point o time, therefore, is considered the cross-sectional study.
Thus, a cross-sectional study is the correct answer.