名词急下降，直下降

noun

1. a change downward

e.g. there was a decrease in his temperature as the fever subsided
there was a sharp drop-off in sales

Synonym: decreaselessening

2. a steep high face of rock

e.g. he stood on a high cliff overlooking the town
a steep drop

Synonym: cliffdrop

3. a noticeable deterioration in performance or quality

e.g. the team went into a slump
a gradual slack in output
a drop-off in attendance
a falloff in quality

Synonym: slumpslackfallofffalling off