常温下，下列各组离子在指定溶液中一定能大量共存的是（ ） A．pH=1的溶液中：

The ducks _____________ swimming in the river.[ ]

A. am

B. is

C. are

《国家电网公司2011年新建变电站设计补充规定》要求，（）及以上电压等级各间隔合并单元宜冗余配置。

For a well planned project the project schedule is ______.

A) the agenda for carrying out the plan or a portion of it
B) not important, as each team member acts according to plan
C) used to generate a time table of major commitments for the project
D) both A and C

螺杆泵的小修周期为（）。

A.3个月

B.6个月

C.9个月

D.12个月

（）是重大的危险物品。