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这
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这
(pronoun) this; these; (bound form) this; the (followed by a noun); (bound form) this; these (followed by a classifier) (in this sense, commonly pr. zhèi, esp. in Beijing)
是
to be (followed by substantives only); correct; right; true; (respectful acknowledgement of a command) very well; (adverb for emphatic assertion)
我
I; me; my
昨天
yesterday
买
to buy; to purchase
的
of; ~'s (possessive particle); (used after an attribute when it modifies a noun); (used at the end of a declarative sentence for emphasis); (used after a noun, verb or adjective to form a nominal expression, as in 皮革的 (pígéde) "one made of leather" or 跑堂儿的 (pǎotángrde) "a waiter (literally, one who runs back and forth in a restaurant)" or 新的 (xīnde) "new one"); also pr. dì or di in poetry and songs
Particle
书
book; letter; document; to write