1、Finding a needle in a haystack is not an easy task.
在干草堆里找到一根针并不容易。
2、She searched every corner of the house, but the missing key was like a needle in a haystack.
她在屋子的每个角落都搜索了一遍，但是丢失的钥匙就像是大海捞针一样难找。