Are these sentences correct:
1-They built a great wall, as it was done in China.
2-They built a great wall, as was done in China.
3-They built a great wall, as in China.
In which case:
a-The wall was built in the same way as the one in China
and in which case:
b-the wall they built was like the one in China (but was maybe built in a different manner)
and in which:
c-The similarity between the two cases is simply that a great wall was built
First option sounds most natural, however none of them are incorrect.
I'm not a teacher yet, but I am studying a Bachelor of Education with an English Literature major at Charles Sturt University, in NSW, Australia.