下颌下腺开始发育于胚胎（）
A.第5周
B.第6周
C.第7周
D.第10周
E.第12周
参考答案：C
城市污染、环境质量下降的主要表现是
①大气污染和水污染
②交通拥挤和住房困难
③有污染的工业布局不合理
④噪声污染和固体废弃物污染
A．①④
B．①③
C．②③
D．②④
The parties to government procurement refer to the principal entities of all kinds that enjoy rights and undertake obligations in government procurement, including the procuring entities,the () and the procuring agencies.
A、users
B、servers
C、producers
D、suppliers
