混凝土结构施工时，对模板有三个方面的要求，分别是什么？
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Which of these words almost always have a weak pronunciation? (select all that are correct)
A. a
B. of
C. can't
D. and
Can is usually unstressed when _________.
A. when another word follows it in a sentence.
B. it is at the end of a sentence.
/ə/ is the least common vowel sound in English.
A. 对
B. 错
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