折射仪不能区分某些合成宝石,如天然红宝石与合成红宝石。
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Complete the following sentences with proper prepositions or adverbs.After being together _____ years, the couple can’t bear to part from each other.
Complete the following sentences with proper prepositions or adverbs.Students can pick _____ BBC English programs with a short-wave radio.
Complete the following sentences with proper prepositions or adverbs.My mother will be responsible ____ the kids when we are away.