a precautionary measure的用法和样例：
- He was kept in hospital overnight as a precautionary measure.
- Police in riot gear were in attendance as a precautionary measure.
- That yellow ambulance is there all day. I guess it's a precautionary measure for any emergency on the ski hill.
- Because emerging economies' supply of financial instruments is so unreliable, people may hoard more of them as a precautionary measure.
- The omission of Cristiano Ronaldo from United's squad to face Glentoran on Wednesday is merely a precautionary measure against a minor ankle injury.