Thay say that Mr Liu can speak German .

Thay say that Mr Liu can speak German .
Thay say that Mr Liu can speak German .=It's said that Mr Liu can speak German.为什么是say的过去式呢?（2）宾语从句里why=what for 另外2个好象是where= 还有一个我忘了能不能告诉我?我以后能问你英语吗?