起先我不知道发生了什么事。

I didn't know what had happened.

youdao

我不知道发生了什么事，但我可以猜出来。

I don't know what passed, but I can guess.

youdao

但是有一天，放学回家后，我妈妈走进卧室，躺在床上。我不知道发生了什么事。

But one day, after we got home from school, my mother went into the bedroom and stayed in bed. I didn't know what had happened.

youdao

I don't know what happened. She is bleeding.

我不知道发生了什么事。她正在流血。

I will实战 - SpeakingMax英语口语达人