从供选择的答案中选出应填入英语文句中()内的正确的答案。 Software design is a(A) process. It requires a certain (B) of flair on the part of the designer. Design can not be learned from a book. It must be practiced and learnt by experience and study of existing systems. A well (C) software system is straight forward to implement and maintain, easily (D) and reliable .Badly (C) software systems, although they may work are (E) to be expensive to maintain, difficult to test and unreliablE. A: ① create ② created ③ creating ④ creative B: ① amount ② amounted ③ mount ④ mounted C: ① design ② designed ③ designing ④ designs D: ① understand ② understands ③ understanding ④ understood E: ① like ② likely ③ unlike ④ unlikely