To solve this question, the user needs to know the basic syntax of Python and the behavior of the append() method.

The given code creates a list named numbers containing the integers 1, 2, 3, and 4. The append() method is then called on the numbers list, with the argument [5, 6, 7, 8]. This will add the entire list [5, 6, 7, 8] as a single element at the end of the numbers list.

So, after the append() operation, the numbers list will contain 5 elements: [1, 2, 3, 4, [5, 6, 7, 8]]. Finally, len(numbers) is called to get the length of the list, which is 5.

Therefore, the answer is:

The Answer is: B. 5