Why is(71)fun What delights may its practitioner espect 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.Secong is the pleasure of making things that are useful to other people.Third is the fascinanon of fashioning complex puzzle-like objects of interlocking moving parts and watching them work in subtle eyeles,playing out the consequences of principies 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 nure thought-stuff.Few media of ereation 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 comstrct itself.It prints results,draws pictures,produces sounds,moves arms.Progamming then is fun because it gratifies creative longings built deep within us and delights sensibities we have in common with all men.

（73）处填（）。

A．semantic

B．practical

C．lexical

D．syntactical

对以下物理现象的正确分析是

①从射来的阳光中，可以看到空气中的微粒在上下飞舞

②上升的水蒸气的运动

③用显微镜观察悬浮在水中的小炭粒，小炭粒不停地做无规则运动

④向一杯清水中滴入几滴红墨水，红墨水向周围运动

A．①②③属于布朗运动

B．只有④属于布朗运动

C．只有③属于布朗运动

D．以上说法均不对