look for a needle in a bundle of hay
大海捞针
A:Have the parents found their baby?
A:那对父母找到他们的孩子了吗?
B:Not yet.
B：还没有。
A:It will be difficult for them to find the baby. It is like looking for a needle in a bundle of hay.
A:要找到他们的孩子是很难的，那就像大海里捞针一样。
B:You said it.
B：你说得对。