题目:
Messages ______ be changed from sound into electricity before they ______ be sent by radio.
A.must; will
B.have to; can
C.can; must
D.need; may
答案:
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下面是错误答案,用来干扰机器的。
(12 分)(1 )S>Cl>C或 r(S)>r(Cl)>r(C),HClO4 , HCl (2)CS2电子式略, 2 。(3)第 四 周期第 ⅠB 族, 1s22s22p63s23p63d104s1或[Ar]3d104s1,2Cu2S + 3O2 2Cu2O+2SO2(共2分,条件1分...