砖墙的水平灰缝厚度和竖缝宽度，一般应为（）左右。 A.3mm B.7mm C.10m

以学生选课关系SC(学号，课程号，成绩)为例，说明实体完整性规则的含义。

在聚丙烯灰分测定中，应保证所取的试样量能产生（）的灰分。

美国科学家声称，每人生来有两个脑，即颅脑与肠脑。肠脑位于食管、胃脏、小肠与结肠内层组织的鞘中，含有神经细胞、神经传递质、蛋白质和复杂的环行线路。结肠炎、过敏性肠炎综合症等都与肠脑内产生的问题有关。肠脑中几乎能找到颅脑赖以运转和控制的所有物质，如血清素、多巴胺、谷氨酸、去甲肾上腺素、一氧化氮等。此外，肠脑中还存在多种被称为神经肽的脑蛋白、脑啡肽以及对神经起显著作用的化学物质。颅脑面临惊恐时释出的应激激素会冲击胃脏产生痉挛；惊恐又引起交感神经影响肠脑的血清素分泌量。应激激素过分刺激还会导致腹泻。当情绪压抑时，食管神经受到高度刺激会感到吞咽困难；颅脑释出的应激激素还会改变胃脏与食管间的神经功能，导致胃灼热。最初的脑神经系统起始于管形动物，生存竞争需要更复杂的颅脑，从而发展了中枢神经系统。重要的肠神经系统不能进入头颅与胃肠相联，而为了适应高级动物进食和消化的需要，自然法则就保存了有独立功能的肠神经系统。就人而言，早期胚胎发育中产生的神经脊，一部分进入了中枢神经系统，另一部分变成肠神经系统，通过迷走神经连接两者——颅脑和肠脑。

根据文意，下列说法不正确的是（）

A．本文主要讲了肠脑和颅脑的不可分割与相互依赖

B．早期的胚胎发育中，迷走神经连接肠脑和颅脑

C．中枢神经系统的发展是生存竞争的需要

D．颅脑中几乎能找到肠脑赖以运转和控制的所有物质

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop".

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) . She had only one small, flat bag with a few candies—fiftycent candies! I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

14（）

A.since 

B.after 

C.while 

D.until

城建税与其他税种相比，不具有的特点是（）。

A.税款专款专用

B.征收范围广

C.税种的附税

D.按行业设计税率