（4+27）×25=4×25+27______．

用所给出的词选词填空，每个词只能用一次。

prefer, provide, hand, out, realize, sweet, reminds, cook, came up with, rush, salty, looking for, saving

1. I              classical music to pop music.
2. Could you              me with information about student exchange programs?
3. Be quiet please, class. I'm going to              your test papers.
4. I was waiting for the school bus but it didn't come. Then I             it was Saturday.
5. I don't like eating chocolate. The taste is too             .
6. That man              me of my English teacher. They wear the same clothes.
7. My mother is going to              Beijing Duck tonight. Would you like to come for dinner?
8. My friend Dave              a great idea! We're going to make a pen pal web site.
9. I woke up late this morning. I had to really              to get to school on time.
10. Mom added salt but it still wasn't              enough.
11. We're              a quiet place to go on vacation. Do you know a good place?
12. I'm              my money so I can buy a new bicycle.

以下关于sIgA叙述，错误的是（）

A.由血液进入唾液

B.诱导细菌间的凝聚，抑制其在黏膜表面和牙菌斑的黏附

C.与病毒表面受体结合，抑制病毒与宿主细胞膜的融合而阻止病毒进入细胞

D.激活补体C3旁路和调理作用

E.抑制细菌酶活性，干扰细菌代谢

如图所示为一磁流体发电机示意图，A、B是平行正对的金属板，等离子体（电离的气体，由自由电子和阳离子构成，整体呈电中性）从左侧进入，在t时间内有n个自由电子落在B板上，则关于R中的电流大小及方向判断正确的是（　　） A．I= ，从上向下 B．I= ，从上向下 C．I= ，从下向上 D．I= ，从下向上

如果用llink-rlink法存储该二叉树，则各结点的指针域中共包含( )个空指针。

车细长轴时，跟刀架的卡爪压得过紧，出现（）

A.锥度

B.多棱形

C.竹节形