前面加介词for，例如：
1、So， if you want to keep your parasol long-term， prepare another umbrella for rainy days 。所以，如果想延长遮阳伞使用寿命，下雨天还是准备其他伞吧。
2、I'll put the rest in the bank for a rainy day.我要把余款存入银行以备不时之需。
3、They have a little nest egg tucked away somewhere for a rainy day.他们把一小笔钱存在了什么地方，以备不时之需。
