expert前加什麼冠詞

前面加冠詞an，例如：

1、We employ an expert to advise on new technology.我們聘用了一位專家擔任新技術顧問。

2、He earned a reputation as an expert on tax law.他贏得了稅法專家的美名。

3、An expert with a trained eye will spot the difference immediately.訓練有素、眼光敏銳的專家會馬上發現差別所在。