What's about operas according to the second paragraph
A. The characters in operas don't act but sing.
B. The stories of opera are only about love.
C. The stories of opera may have either happy ending or sad ending.
D. The characters in the opera speak to tell the stories.
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某料成本系料1.8，若购进单价为18元/kg的同质量的原料8kg，此料的单位成本是14.4元/kg。（）
A. 对
B. 错
I had been working a couple of months ______ I had a letter from Mike.
A. when
B. until
C. that
D. while
The author doesn't think it good wearing red sweaters if ______.
A. the crowd do it
B. you can't afford them
C. you don't look good in red
D. the situation isn't safe
Football, or ______ soccer in Britain, is the most popular sport in the world.
A. called
B. it is called
C. what is called
D. something calls
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