【俚語】

Back off 退后

【例句】

Back off！Don’t touch me！
后退！別碰我！

Step back 退后

【例句】

Please step back from the injured woman. Give her some air.
不要靠近受傷的女士，請往后退一點，讓她透透氣。

Keep back! 退后

【例句】

"Keep back!" he shouted, "Don't come any closer!”
“退后！”他大叫著，“不要再靠近了！”

Back and forth
反復地；來回地

【例句】

During the party, I went back and forth to the kitchen to get drinks for the guests.
在聚會上，我來來回回從廚房給客人們拿飲料。

Back in the day
曾幾何時

【例句】

Back in the day, I used to spend my summers exploring or playing with friends. Now I'm in the office every day.
曾幾何時，我常常在夏天和朋友們玩或者去野外探索。現在我每天都只能在辦公室。