我正在走回家，突然就下起了倾盆大雨。

I was walking home, and ___the ___next ___thing ___I ___knew, it started pouring rain.

她正在讲笑话，突然大家都狂笑不止。

She was telling a joke, and ___the ___next ___thing ___I ___knew, everyone was laughing hysterically.

我们正在平静地聊天，突然警报响了。

We were chatting peacefully, and ___the ___next ___thing ___I ___knew, an alarm went off.