什么叫做操作弹性？

a※b是新规定的这样一种运算法则：a※b=a²+2ab，若（﹣2）※x=8，则x=（    ）．

大华商场委托飞达广告公司制作了一块宣传企业形象的广告牌，并由飞达公司负责安装在商场外墙。某日风大，广告牌被吹落砸伤过路人郑某。经查，广告牌的安装存在质量问题。关于郑某的损害，下列哪一选项是正确的( )

A．大华商场承担赔偿责任，飞达公司承担补充赔偿责任

B．飞达公司承担赔偿责任，大华商场承担补充赔偿责任

C．大华商场承担赔偿责任，但其有权向飞达公司追偿

D．飞达公司承担赔偿责任，大华商场不承担责任

港口本身属于港口城市最重要的交通基础设施之一，在港口城市对外和对内交往中起着关键作用。

能引起土壤酸性的离子有（）。

A、H⁺

B、Ca²⁺

C、Mg²⁺

D、A1³⁺

E、Na²⁺

Solving a problem can be broken down into several steps. First, the problem must be identified correctly. Psychologists refer (1) this step as problem representation. For many problems, figuring (2) which information is relevant and (3) is extraneous can be difficult and can interfere (4) arriving at a good solution. Clearly, before a problem can be solved, it must be obvious (5) the problem is, however, this is not as easy (6) it might seem. One obstacle to efficient problem representation is functional fixedness, that is, allowing preconceived notions and even prejudices (7) color the facts. Most people tend (8) see objects and events in certain fixed ways, and by being inflexible in viewing the problem, they may be unable to notice the tools (9) the solution. Once the problem is identified accurately, (10) , the second step consists (11) considering the alternatives for a solution. A common way to evaluate alternatives is to write them (12) and then make a list (13) advantages and disadvantages for each solution. Here again, people may be limited by prior experiences. Often people adopt mental sets (14) lead them to the same problem-solving strategies that were successful for problems (15) the past. Although that can be helpful most (16) the time, sometimes a new situation requires a different strategy. (17) that case, the mental set must be abandoned, (18) new alternatives must be explored.
After the alternatives have been compared, a strategy must be selected (19) among them. One way to avoid becoming mired in the options is (20) try the best option with a view to abandoning it for another (21) the results are unfavorable. This attitude allows many people to move on expeditiously (22) the next step—action. The strategy selected must be implemented and tested. If it solves the problem, no further action is necessary, but if (23) , then the cycle begins again, starting (24) problem identification. By continuing to review the problem (25) repeat the problem-solving steps, the solution can be improved upon and refined.