XVF电梯某个楼层指令按钮不亮，会是哪些原因？
参考答案：
该楼按钮开关或按钮线有问题；
该楼按钮灯损坏或按钮灯线不通；
PLCI/O模块对应点损坏。
Daniel is helpful, and he always_______. [ ]
A. thinks of himself first
B. thinks of others first
C. thinks himself first
D. thinks others first
计算机最基本、最重要的系统软件是__________。
