皮皮学，免费搜题
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搜题
【单选题】
气雾剂的组成不包括A.
抛射剂
B.
药物与附加剂
C.
硬化剂
D.
耐压系统
E.
阀门系统
拍照语音搜题，微信中搜索"皮皮学"使用
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】— There'ssomeone knocking on the door. Who _____it be? — It must be Mary. She promised to be here at 8：00.
A.
must
B.
need
C.
shall
D.
Can
【单选题】It promised to be a more difficult ____ than might appear at first sight.
A.
indication
B.
obligatioin
C.
duty
D.
undertaking
【单选题】—There's someone knocking on the door．Who it be? —It must be Mary．She promised to be here at 8：00．
A.
must
B.
can
C.
shall
D.
need