HSK 4
底
dǐ名
bottom; base; background; foundation; copy (of a manuscript or receipt etc) kept as a record; (suffix) end of a year or month; (math.) radix; base (abbr. for 底数)
我在包底找到了钥匙。
Wǒ zài bāo dǐ zhǎo dào le yào shi.
I found the key at the bottom of the bag.
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New in the HSK 3.0 word list at level 4.