Enthuware

Looking forward to the answer to this one, seeing as all five of the options compile

Did you read the detailed explanation provided with it?

Mere successful compilation is not the objective here.

Hi,
No; at the time I was still doing the test (I work through each question, coding examples and testing them (as necessary i.e. in the event of any doubt) as I go, which means I learn twice: once as I take the "test" and again as I recap in going through all the answers). I
I knocked up a small test program for all the possible answers because it seemed to me that all of the options "may" be inserted, by which I take/took to mean, if they are inserted, compilation will not fail. The question should be more precise (I hate saying this because you guys do an amazing job but I have to be honest about the question): "may be inserted" is not the same as "compiles and runs without exception and satisfies the equals() contract", or even just "satisfies the equals contract". It's just a bit...ambiguous
Cheers.

The problem statement has been modified to make it clear now.

Thank you for your feedback!