23. Often he _________ sit for hours doing nothing at all when he was in low spirits.

It’s said that the early European playing-cards ______ for education

Rarely ______ so heavily in Ning Xia as it did in Hei Long Jiang last year.

Whatever work you are doing, you shouldconcentrate your attention ______it.

The manager promised to keep us______ of how our business was going on.