听力原文： Cross was what people call a mystery man. We had known him for over five years, ever since he became a member of our modest club, but he had a way of keeping his private life to himself in all but unessential details. We knew his address, though he did not ever invite us to his home, and his age too, but only insignificant matters of this kind. It appeared that he did not have to work for a living as we did in our various ways. He had once hinted at an inheritance on which he managed to live comfortably. He was not, however, a man of luxurious habits: he was not especially well-dressed and he did not even possess a car. At the age of forty-five he was still a bachelor. Since marriage was not a subject he ever discussed, we had no means of finding out whether he regretted the lack of a wife.
Cross disappeared abruptly from our circle and shortly after we came to learn the first really solid facts about our mystery man. From reports that appeared in the newspapers, accompanied by photographs of man who was, without any doubt, our Mr. Cross, it was revealed that he was a most accomplished burglar, operating chiefly in the London area. He had practised this profession for many years, until he was arrested and sent to prison.
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A. Because he didn't tell us his address.
Because he didn't tell us his age.
C. Because he didn't invite us to his home.
D. Because he kept his private life a secret.