at command的用法和樣例：
例句
- She has a large English vocabulary at her command.
她能靈活運用掌握的大量英語(yǔ)辭匯。 - The sense of this word is hard to come at.
這個(gè)詞的意思不容易掌握。 - Here Mr. Casey had placed at my disposal the agreeable villa he was using.
這里，凱西先生把他自己居住的那座舒適的別墅供我自由使用。 - Users can make their public keys freely available or place them at a key distribution centre for others to access.
用戶(hù)可以讓公開(kāi)密鑰自由使用或者把公開(kāi)密鑰放在可由別人存取的密鑰分配中心。
