We have stayed at this school for _______ 。Which following choice is wrong?
A. two and a half years
B. two years and a half
C. two years and half a year
D. both A and B
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Which ARE right?
A. 2009, June 25
B. 25th June, 2009
C. June 25, 2009
D. June 25st, 2009
下列化合物无光学活性的是
A. ClCH=C=CHCH3
B. CH3CH=C=CHCH3
ClCH=C=C(CH3)2
D. CH3-CH(Cl)-CH=CH2
化合物有手性的主要判断依据是分子中不具有
A. 对称轴
B. 对称面
C. 对称中心
D. 对称面和对称中心
关于苯分子结构下列说法正确的是
A. 单、双键交替的环己三烯型结构
B. 6个电子离域在六个碳形成的环上的共振杂化式
C. Kekulé结构式
D. 以上都是
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