See the flags on top of the building? That was _______ we did this morning.(2006年全国I高考题)
Hie risk of heart disease is a powerful argument ___________ smoking.
It is a serious novel, not ___________.
We go for a walk in the fields ___________, but not often.
Don't be rude to your father. Never in his life ___________ that way.
It seems that living green is ___________ easy and affordable. A small step makes a big difference.