I couldn't understand the people.They talked fast.（合并为一句）

I couldn't understand the people.They talked fast.（合并为一句）
I couldn't understand the people.They talked fast.（合并为一句）

I couldn't understand the people.They talked fast.（合并为一句）
I couldn't understand the people because they talked fast.
或者：they talked fast so that i couldn't understand the people.

i couldn't understand the people who talked fast.

I couldn't understand the people because they talked fast