The verbs 'overheard' and 'attended', though grammatically correct at 'A' and 'B', respectively, do not fit contextually because one cannot 'overhear' a whole festival and 'attend' is usually not used with conversation. Thus, if we interchange words 'A' and 'B', the sentence becomes contextually sound.
The word 'C' is contextually and grammatically correct at its position since it is preceded by a definite article and is a noun.
The correct order is BAC. Hence, the correct answer is option (d).
Correct statement after corrections: Simone, who attended the whole festival at the same time, came across her during the interval and overheard a conversation about her sparked by her response to the famine in China.