皮皮学，免费搜题
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【单选题】
下列属于常用的成膜材料的是A.
PVA
B.
CMC
C.
EC
D.
PEG
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参考答案：
参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】We ____ here two hours ago . We ____ here for two hours . [ ]
A.
have arrived, have been
B.
have come, have been
C.
came, have come
D.
arrived, have been
【简答题】请简述交换机的数据转发规则。
【简答题】We appear to have been given the wrong address. as It ____________________ we have been given the wrong address.
【简答题】昆虫内共生菌在哪些细菌类群中分布较多?
【单选题】We ______ for you everywhere. Where have you been?
A.
have looked
B.
looked
C.
have been looking
D.
are looking