Final answer:
The research problem that conforms to the textbook author's definition of a good research problem is investigating the correlation between diet and academic performance.
Step-by-step explanation:
The research problem that conforms to your textbook author's definition of a good research problem is b) Investigating the correlation between diet and academic performance. This research problem is specific, measurable, and has clear variables to study.
The problem is the correlation between diet and academic performance, the students' diet is the independent variable, and their academic performance is the dependent variable. By studying this correlation, researchers can gain valuable insights into the impact of diet on academic performance.
For example, a researcher could collect data on students' diets and their grades, and then analyze the data to determine if there is a significant correlation between the two variables.