四
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儿
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囗
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Mnemonic symbol: a four-leaved clover. Socrates (s) is working out in the bathroom of the space station (Ø4). He's lifting four (四) wooden boxes (囗), and wonders why they are so heavy. He doesn't know that inside one of the four boxes, the monkey king (儿) is hiding and secretly laughing at him - until the monkey king comes out and surprises Socrates with a four-leaved clover (四).
Sherlock Holmes (sh) started a supermarket (市) in the space station's bathroom (Ø4), but all he has for sale right now are berets (亠) and towels (巾). He should have opened it at the beach!