肽聚糖种类的多样性主要反映在（）结构的多样性上。
A、肽桥
B、黏肽
C、双糖单位
D、四肽尾
参考答案：A
面粉厂的碾磨工段火灾危险性应划为()。
A．甲类
B．乙类
C．丙类
D．丁类
My uncle now teaches French in a famous domestic university, who _______ in Paris for 6 years.
A．have lived
B．lived
C．was living
D．had lived
