What is the property of InnoDB that enforces foreign key relationships stay intact?

This question is about how MySQL's InnoDB storage engine makes sure that data relationships stay correct. Let's break down the options:
Option A: Atomicity - This means that a transaction (a set of changes) is either completely done or not done at all. It's like a bank transfer: either all the money moves, or none of it does.
Option B: Durability - This means that once a transaction is complete, the changes are permanent and will be saved, even if the database crashes. It's like writing something in stone – it's there to stay.
Option C: Consistency - This means that the database follows rules and constraints to ensure data accuracy. It's like making sure your math equations always add up correctly.
Option D: Referential Integrity - This is the key! It's a set of rules that guarantee relationships between tables are always valid. Imagine a table of students and a table of classes. Referential integrity ensures that every student in the "students" table has a valid matching class in the "classes" table.
So, the answer is Option D: referential integrity. It's the specific property that InnoDB uses to make sure those relationships are always valid.