I was doing my homework.My mother came back.合并为一句

I was doing my homework.My mother came back.合并为一句

When I was doing my homework,my mother came back

not until my mother came back,i did my homework. 这个句子有错误，后面应该是did i do my homework. 这是一个倒装强调句型，后面的这是主句，前面是状语从句。两者的时态要保持一致。 后面的那个是正常语序，两者的时态也要一致。

I was doing my home work whem my mother came back.

while I was doing my homework ,my mother came back . I was doing my homework when my mother came back

While I was doing my homework ,my mother came back . I was doing my homework when my mother came back . The moment my mother came back, I was doing my homework.