X、Y、Z三种元素，原子序数依次减小。X是第四周期主族元素，其部分电离能如图所示；X、Y元素具有相同的最高正化合价；Z原子价电子排布式nsⁿnpⁿ。回答下列问题：

（1）X原子的电子排布式为                      。

（2）电负性：X     Y（填“＞”、“=”或“＜”）。

（3）元素Z的一种氢化物（化学式为Z₂H₄）是重要的化工原料。     有关Z₂H₄分子的说法正确的是          （填字母）。

A．分子中含有氢键

B．属于非极性分子

C．含有4个σ键和1个π键

D．Z原子的杂化方式为sp²

（4）X的氧化物与钛（Ti）的氧化物相互作用，能形成钛酸盐，其晶体结构如图所示（X、Ti和O三种元素对应的离子分别位于立方体的体心、顶点和面心）。该晶体中，钛离子和周围      （填数字）个氧离子相紧邻。

（5）NH₄Cl晶体中含有多种化学键，其中一定不含有的化学键是          （填字母）。

A．离子键       B．非极性键     C．配位键       D．金属键

Motherhood may make women smarter and may help prevent dementia in old age by bathing the brain in protective hormones, US reseachers reported on Thursday.
Tests on rats show that those who raise two or more litters of pups do considerably better in tests of memory and skills than rats who have no babies, and their brains show changes that suggest they may be protected against diseases such as Alzheimer’s. University of Richmond psychology professor Craig Kinsley believes his findings will translate into humans.
"Our research shows that the hormones of pregnancy are protecting the brain, including estrogen, which we know has many neuroprotective effects, " Kinsley said.
"It’s rat data but humans are mammals just like these animals are mammals, " he added in a telephone interview. "They go through pregnancy and hormonal changes. "
Kinsley said he hoped public health officials and researchers will look to see if having had children protects a woman from Alzheimer’s and other forms of age-related brain decline.
"When people think about pregnancy, they think about what happens to babies and the mother from the neck down, " said Kinsley, who presented his findings to the annual meeting of the Society of Neuroscience in Orlando, Florida.
"They do not realize that hormones are washing on the brain. If you look at female animals who have never gone through pregnancy, they act differently toward young. But if she goes through pregnancy, she will sacrifice her life for her infant—that is a great change in her behavior that showed in genetic alterations to the brain. \

"It’s rat data but humans are mammals just like these animals are mammals. "
What does the sentence suggest

A. The experiments on the rats have nothing to do with humans.
B. The experiments on the rats are very important for animals.
C. The experiments on the rats are much the same on humans.
D. The experiments on the rats are much the same on other animals.