房地产买卖交易的最后一步是（）。
A.物业交验
B.合同签订
C.款项支付
D.合同备案登记
参考答案：A
.
The Bank of China, having so far woven its network in 27 countries, ______ its business in Brazil in June 2009.
A．has started
B．was starting
C．will start
D．started
下图是实验室常用的气体制备、收集、检验的多功能装置．
（1）图中甲装置常用于制取氧气，其反应的化学方程式是______；利用甲装置还能制取______气体．
（2）若在乙装置中盛满水，用排水法收集（瓶口向上）一瓶氧气，气体从______端（填字母“a”或“b”）通入．
（3）某同学用排水法收集一瓶氧气，将带火星的木条伸入集气瓶中，木条不复燃，原因可能是______．
The Bank of China, having so far woven its network in 27 countries, ______ its business in Brazil in June 2009.