21.   But for some unknown reason, Susan never became pregnant.

22.   But for unknown reasons, Nicholaus decided to turn himself and Brian in while at a gas station across the street from the Grants Pass police station.

23.   But for unknown reasons, Yeltsin was unwilling or unable to fulfill that pledge.

24.   But for the last two years, for some unknown reason, only a few thousand have wintered here.

25.   But for unknown reasons, the degree of risk reduction was lower among Latinas, said Dr. Gary M. Shaw, the principal researcher in the study.

26.   But, for some unknown reason, things never arrived.

27.   City water officials said the boiler automatically shut down over the weekend when it malfunctioned for unknown reasons.

28.   Each time the cell divides, it is liable for unknown reasons to miscopy the sequence by inserting an extra chemical letter before or after it.

29.   For an unknown reason, there were two copies of this very column.

30.   For an unknown reason, two men inside that car opened fire.