Software design is a (46) process. It requires a certain amount of fl air on the part of the (47) . Design can not be learned from a book . It must be practiced and learnt by experience and study of existing systems. A well (48) software system is straightforward to implement and maintain , easily (49) and reliable. Badly (48) software systems, although they may work are (50) to be expensive to maintain , difficult to test and unreliable.

A．designer

B．user

C．computer

D．design

伸肘时，肌肉活动情况为

A．肱二头肌、肱三头肌同时收缩

B．肱二头肌、肱三头肌同时舒张

C．肱三头肌收缩，肱二头肌舒张

D．肱三头肌舒张，肱二头肌收缩