IF THERE ISN'T ENOUGH RAIN, THE HYDROPOWER STATION CAN NOT OPERAT...

42. If there isn't enough rain, the hydropower station can not operate.

A. When there isn't enough rain, the hydropower station can operate.

B. Unless there isn't enough rain, the hydropower station can not operate.

C. Unless there is enough rain, the hydropower station can operate.

D. Unless there is enough rain, the hydropower station can't operate.