发电机与电网同步的条件，主要是指（）
A、相序一致
B、相位相同
C、频率相同
D、电压大小相等
参考答案：A, B, C, D
China will spend about 52 billion yuan ______ new airports and ______ old ones in the west of China in the llth Five-Year Plan period. [ ]
A. repairing ; building
B. to build ; repair
C. building ; repairing
D. to repair ; build
