挡箭牌
【注音】dǎng jiàn pái
【解释】挡箭牌就是盾牌。当一种东西被用来作为借口，它就是挡箭牌；当一个人被用来遮护别人，这个人也就成了挡箭牌。
When something is taken as a pretext, you can call it a shield; similarly, when somebody was used as a protector, you can also call the person a shield.
【例子】
例：“太忙了”是一个很好的挡箭牌。
Ex.：“Too busy” is a good excuse.

导火线
fuse
【注音】dào huǒ xiàn
【解释】爆炸物的引线，比喻引发事件的事件。
Blasting fuse is often used as a metaphor for a small incident that touches off a bug one.
【例子】
例：老谢夫妇吵架了，儿子的成绩不好是导火线；实际上是因为他们俩对赡养老人在看法上有分歧。
Ex.：Their son’s poor score started a bitter quarrel between the old couple of Xie; but actually the real reason behind is that they can’t agree with each other on supporting their old parents.