海底撈針

hǎidǐlāozhēn

fish for a needle in the ocean; look for a needle in a haystack

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hai3 di3 lao1 zhen1

see 大海撈針, 大海捞针

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海底撈針|海底捞针 [hǎi dǐ lāo zhēn] ► see ↑大海撈針|↑大海捞针 [dà hǎi lāo zhēn]