提高程序的可读性和易维护性的关键是使程序结构______。
参考答案：简单清晰
．The letter Mary had looked forward to ____her last night and she was very excited．
A．reached
B．reaching ’
C．had reached
D．has reached
车身机械磨损，磁撞挤压等损坏，通常采用（）、（）接的方法修理：腐蚀和反复施焊的损坏，通常采用拆除、更新的方法修理。
