Why is (71) fun What delights may its practitioner expect as his reward First is the sheer joy of making things. As the child delights in his mud pie, so the adult enjoys building things, especially things of his own design. Second is the pleasure of making things that are useful to other people. Third is the fascination of fashioning complex puzzle-like objects of interlocking moving parts and watching them work in subtle cycles, playing out the consequences of principles built in from the beginning. Fourth is the joy of always learning, which springs from the (72) nature of the task. In one way or another the problem is ever new, and its solver learns something: sometimes (73) , sometimes theoretical, and sometimes both. Finally, there is the delight of working in such a tractable medium. The (74) , like the poet, works only slightly removed from pure thought-stuff. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures.
Yet the program (75) , unlike the poet’s words, is real in the sense that it moves and works, producing visible outputs separate from the construct itself. It prints results, draws pictures, produces sounds, moves arms. Programming then is fun because it gratifies creative longings built deep within us and delights sensibilities we have in common with all men.

A．semantic

B．practical

C．lexical

D．syntactical

纯净的CaCO₃可用来测定盐酸的浓度．采用适当的试剂，从石灰石（主要成分为CaCO₃）获得高纯度CaCO₃的流程如下：

试回答：

（1）气体B的化学式为______，产生B的反应属于______反应（填基本反应类型）．

（2）写出CaCO₃与盐酸反应的化学方程式______．

（3）使原料中各原子的利用率尽可能达到100%，是“绿色化学”的核心理念之一．上述流程中有的物质可以再利用，请在流程图上用箭头标示再利用的路线（箭头要求：从可利用的物质出发，指向利用该物质的环节）．