Final answer:
The main idea of the given sentence is about using foil on an oven rack to catch any overflowing pie filling during baking.
Step-by-step explanation:
The main idea of the sentence "An oven rack lined with foil can catch pie filling that may boil over" is that covering an oven rack with foil can be used as a preventative measure to catch any overflow of pie filling when baking a pie.
This statement combines two concepts: the possibility of pie filling boiling over and the use of foil to catch it if it does. Although options (A), (B), and (D) each touch on parts of the process, option (C) is the most complete as it connects both the problem and a potential solution.