◆on guard站岗;值班;警戒
Police were on guard at Barnet Town Hall.警察在巴尼特市政大厅站岗执勤。
to be on your guard against sth or to be on guard against sth
+ attack, criticism提防某事物;警惕某事物
He is constantly on guard against any criticism.他时刻提防着任何批评。
Everyone should now be on their guard against terrorist attacks.每个人现在都要提防恐怖袭击。