The first two events have only happened once in the 90s.

So you may hear about the same thing for a few days, even though it only happened once.

And you're saying this might happen once a day for the next several, if not 18, days?

This practice only happened once a year until the past 10 years.

It may happen once every couple of weeks, or four times a day.

This has, however, only happened once without someone else taking up the role.

They never had more than a 1-point lead, and that happened just once.

This happened to us once, and look at our situation.

It's probably happened to everyone in Israel at least once.

But if that kind of thing only happened once in a while, I could put up with it.