Have to agree with UMG Developer. The "Multiple identifier columns" shouldnt be part of the answer for 2 reasons.
1. Its not part of MS recommendations (atleast not on the page thats linked in the answer)
2. In the answer you have yourself added
While having multiple identifier columns is not, strictly speaking, against the rules, it makes the table design overly complex, wastes space and adds no value
So your contradicting yourself. Now i do agree that that might not be the best solution but that doesnt make it wrong.
Although i did select the "Nullable columns" option as well i dont really agree with that. It sounds nice in "theory". But from a practical point of view its not. Because if your building a system that will have ANY form of human interaction it just wont work. Unless you want to put every datacolumn into its own table and have tables like CustomerSurName/CustomerLastName/CustomerMiddleName. Instead of just CustomerName. This is one "rule" that should be used real sparingly.
/T