Which line of code correctly asserts that the sumArr method returns the expected sum?

The option that correctly asserts that the sumArr method returns the expected sum is the one that utilizes console.assert with the proper condition being checked. This method is specifically designed to log an error message to the console if the assertion provided evaluates to false.

In this case, if the expected sum is 9, using console.assert(res === 9); effectively checks if the actual result stored in res is equal to 9. If res does equal 9, no message is printed, indicating that the method has returned the expected value. However, if res does not equal 9, an assertion error will be logged, providing feedback that the sumArr method did not return the correct sum.

This makes console.assert(res === 9); a valuable tool for debugging, as it allows you to confirm the expected outcome during development without cluttering the console with messages unless there's a failure. Thus, it provides an efficient way to ensure the functionality of the method behaves as intended.