sign up: 签字，报名
Many people who sign up to facebook quickly find they have no use for it.
很多在facebook上注册的人很快就会发现，他们根本用不上它。

show up: 显而易见，到场
He went sailing and did not show up for a long time.
他航行去了，而且很长一段时间没有露面。

pop in: 突然出现
He said he'd pop in and see us when he got back.
他说回来后顺道来拜访。

break off: 结束，分手
I promised to break off with her, as long as seeing her again.
我答应和她断绝来往，只要再见她一面。
We still break off finally.
最后我们还是分手了。