单选题 What caused the blackout in July 1977?

A、 Excessive heat probably made people switch on too many electrical appliances.
B、 Because of unemployment, some machines were not in proper working order.
C、 During a storm, lightning damaged supply cables.
D、 The passage does not mention the cause.

【正确答案】 C

【答案解析】[解析] 导致1977年大停电的原因是暴雨中，闪电损坏了电缆。所以选择答案C。