他婉拒了参加晚宴的邀请，说自己太忙了。

He politely ___declined the dinner invitation, saying he was too busy.

近年来，这座城市的空气质量一直在下降。

The air quality in this city has been ___declining in recent years.

这条小路缓缓向下倾斜，通向村庄。

The trail ___declines gradually as it leads to the village.

随着时间推移，这座老房子的状况开始恶化。

The condition of the old house started to ___decline over time.