hang out 出去玩，闲逛

errand n. 差事，跑腿
I've got a few errands to do in the town.
我有几件事要进城办。
You must do the two errands this week.
你必须在一周内完成这两项任务。
My mother asked me to go on an errand; she wanted me to buy some food.
我妈妈叫我跑一下腿,她想让我去买点食物。

calculus n. 微积分
It's been awhile since I did calculus.
我学微积分已经有一段时间了。
I had studied calculus before I got into college.
我在上大学以前,已经学过微积分。

up to par adj. 达到水平(正常)
I didn't think her performance was up to par.
我认为她表现得不及平时。

unbelievable adj. 难以置信的
They work with an unbelievable speed.
他们以令人难以置信的速度工作。
His ecstasy to the pop music is unbelievable.
他对流行音乐的入迷是令人难以置信的。

convention n. 惯例
The handshake is a social convention.
握手是社交惯例。

start over v. 重新开始
I suggest that you tear up the letter and start over again.
我建议你把这封信撕了，再重头开始写。