光导纤维是由二氧化硅(SiO2)制成的,二氧化碳中硅元素的化合价为()

光导纤维是由二氧化硅(SiO2)制成的,二氧化碳中硅元素的化合价为()

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下列化肥中,从外观即可与其他化肥相区别的是

下列化肥中,从外观即可与其他化肥相区别的是

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The farmer caught a big fish this morning. (改为否定句)The farmer _____ _____ a big f

The farmer caught a big fish this morning. (改为否定句)The farmer _____ _____ a big fish this morning

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I want to be a dentist, because many children don’t ______ (关心) their teeth.

I want to be a dentist, because many children don’t ______ (关心) their teeth.

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