This cat is weak.
It's ____________. [ ]
A. healthy
B. strong
C. sick
答案：C
All flights___ because of the snowstorm, we decided to take the train.
A．were canceled
B．had been canceled
C．having canceled
D．having been canceled
A．，正电荷
B．，正电荷
C．，负电荷
D．，负电荷
，正电荷
，正电荷
，负电荷
，负电荷