追查这个谣言的源头犹如大海捞针。

Tracking down the source of this rumor is like chasing a ___wild goose.

寻找那个失踪多年的宝藏只是一场徒劳的追逐。

Looking for that long-lost treasure is just a ___wild-goose chase.

寻找那个传说中的宝藏完全是在白费力气，它根本不存在。

Searching for that legendary treasure was just chasing a ___wild goose - it never existed.