1.   For some unknown reason, Fred quit his job and moved to Alaska.

2.   For some unknown reason, Mark quit his job and moved to Greece.

3.   For some unknown reason, racial riots during the Depression were almost nonexistent.

4.   For some unknown reason, the blinds were always drawn, giving it a depressing atmosphere.

5.   For some unknown reason, the curtains were always drawn.

6.   For some unknown reason, this plan did not eventuate in a critical edition.

7.   For unknown reasons, a squad of police Marched into the black suburb of Brownsville.

8.   Physically she had a lot more to offer than Kate, but for some unknown reason he really fancied the policewoman.

9.   For some unknown reason, my computer crashed.