锈蚀是指金属材料表面在环境介质的作用下，发生物理变化而遭受破坏的现象。
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Identify the word class:he, she, it, they ,them
A. conjunctions
B. pronouns
C. prepositions
D. verbs
Identify the word class:expensive, extraordinary, economic, colorful
A. adjectives
B. adverbs
C. nouns
D. verbs
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A. adjectives
B. adverbs
C. nouns
D. prepositions
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A. adjectives
B. adverbs
C. verbs
D. nouns
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