I didn't go to his party last night. because _____ I changed my

I didn't go to his party last night. because _____ I changed my mind.
A、on a second thought
B、on the second thought
C、on second thoughts
D、on the second thoughts
【正确答案】：C
【题目解析】：题干译文：我昨晚没有去参加他的聚会，因为经过了进一步考虑之后,我改变了主意。on second thoughts为固定搭配，表示进一步考虑后。答案为C。