I wrote a letter to the car dealer, _____ what had happened to m

I wrote a letter to the car dealer, _____ what had happened to my car.
A、explaining
B、to explain
C、explains
D、explained
【正确答案】：A
【题目解析】：句意：我给汽车经销商写了封信，解释了我的新车出了什么事儿。因为有个逗号,所以这是一句话而不是两句话，主句里wrote是谓语，主句和从句里又没有连接词（例如and,but等），因此从句里的动词不能和主句一样用过去时。explaining在这儿引导了非谓语从句，v-ing形式在句中表伴随或作结果状语，相当于一个并列句。