中国古代都城从周朝开始遵循着从西部到东部地区，再向北部发展的趋势。各个王朝都城的建设

在结构化分析方法中，描述信息在软件系统中流动与处理的图形工具为 【12】 。

阅读下面短文，用所给动词的适当形式填空，使短文完整、通顺。每空不限一词。

Rose is one of the funniest girls in her class. She looks like a boy, and she is good at (1)________ (perform). So she(2) __________(choose) to play Harry Potter by her classmates last week. She said happily, “I’m sure that I (3)_______ ( do )the job well because I(4) __________(see) the movie many times already.”

Dick, one of Rose’s best classmates, is also an actor in the play. He (5)__________(like) to perform the play with Rose. He said, “We are confident that we (6)__________(do) well in our school art festival next week.”

Mrs. Smith, their teacher, pays much attention to their play. She often (7)________(encourage) them. Yesterday afternoon when she(8) __________(watch) their performance, she took photos of them. And the photos (9)_______ (send) to their headteacher next month. They hope their performance (10)_______ (be) the best.

现有含NaCl、Na₂SO₄和NaNO₃的混合物，选择适当的试剂出去溶液中的NaCl和Na₂SO₄，从而得到纯净的

NaNO₃溶液。相应的实验过程可用下图表示

请回答下列问题：

（1）写出实验流程中下列物质的化学式： 试剂X_________，沉淀A________，沉淀B___________。

（2）上述实验流程中加入过量的Na₂CO₃的目的是______________________________________。

（3）按此实验方案得到的溶液3中肯定含有__________（填化学式）杂质；为了解决这个问题，可以向溶液3中加入适量的___________，之后若要获得固体NaNO₃需进行的实验操作是___________（填操作名称）。

德意志谚语说：城市的空气使人自由。这句话对   __最具有吸引力。[ ]

A．商人    

B．封建主    

C．教会    

D．农奴

如果算符函数调用格式的表达式：x.operator-(operator++(y，0)中的“—”是作为成员函数重载的，“++”是作为友元函数重载的，那么该表达式还可以表示为：()

A．x-y++

B．x-(++

C．(x++)-y

D．++x-y