事故 

Pinyin: shìgù 
Meaning：Accident  
Sentence：他否认他应对那个事故负责。He denied that he was responsible for the accident.

More: 

事： 

Pinyin: shì
Meaning: Item; matter; thing
Radical: 亅
Stokes: 8
Traditional: 事
Common words/Phrase:
事件 [shìjiàn] 【event】 
事情 [shìqíng] 【matter】
事宜 [shìyí] 【affairs】
事实 [shìshí] 【fact】
事务 [shìwù] 【affairs】

故： 

Pinyin: gù
Meaning: Old; reason; happening
Radical: 攵
Stokes: 9
Traditional: 故
Common words/Phrase:
故障 [gùzhàng] 【error; fault】 
故意 [gùyì] 【on purpose】
故宫 [gùgōng] 【the Forbidden City】
故乡 [gùxiāng] 【hometown】
故居 [gùjū] 【former residence】