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【单选题】
下列各项中“操作或现象”能达到预期“实验目的”的是 [ ] 实验目的 操作或现象A.
检验碳与浓硫酸反应后的气体产物 将产生的气体依次通过无水CuSO 4 、澄清石灰水和品红溶液
B.
证明蛋白质在某些无机盐溶液作用下发生变性 向鸡蛋清溶液中加入饱和硫酸钠溶液，有沉淀析出；再把沉淀加入蒸馏水中
C.
检验溴乙烷中的溴元素 将少量溴乙烷与NaOH溶液混合共热，充分反应并冷却后,向上层清液中加稀HNO 3 酸化，再滴加AgNO 3 溶液
D.
证明溶液中存在平衡: Fe 3+ + 3SCN - Fe(SCN) 3 将1 mL KSCN溶液与1 mL 同浓度 FeCl 3 溶液充分混合；再继续加入KSCN溶液，溶液颜色加深
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【单选题】听力原文：M: Jeff has not been on good terms with his sister for the last few years, but I hear he visited her on his trip to California recently. W: Yes, he hadn't planned to call on her, but he changed h...
A.
Jeff has always liked his sister.
B.
Jeff made a phone call to-his sister.
C.
Jeff visited his sister.
D.
Jeff planned to visit his sister.
【简答题】电路如图所示，t=0时开关S闭合，S闭合前电路处于稳态。求t＞0时的电流i L (t)和i(t)。
【简答题】电路如图14．35所示。开关S闭合前电路已达稳态。t=0时闭合开关S，用拉普拉斯变换法求电压uc(t)。
【简答题】电路如图所示。t＜0时电路处于稳态，t=0时开关S闭合。求S闭合后的电压u(t)。
【单选题】Sam has curly hair but his twin sister’s is quite ().
A.
even
B.
straight
C.
uneven
D.
regular
【单选题】His sister _____ to the hospital. She will be back _____ half an hour. [ ]
A.
has gone; after
B.
has been; in
C.
has gone; in
D.
has been; after
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