However the incident was the only sparkthe fire.A. which set offB. set offC. that set offD

问题补充：

However,the incident was the only sparkthe fire.

A. which set off

B. set off

C. that set off

D. setted off

答案：

A. which set off

B. set off

(答案→)C. that set off

D. setted off

解析：考查定语从句。本题定语从句的先行词是the only spark，因为先行词前面有only修饰，且是表示物的名词，后面使用关系代词that指代先行词在 句子做主语。句意：然而，这个小事情是引起火灾的唯一的原因。根据句意说明C项正确。