Dear Hans and Otared,
Thank you for the reply.
I tried "%!TEX root =“ with no space before but it does’t work.
I think that ConTeXt doesn’t do anything as you said.
The strange thing is that it worked in ConTeXt file sometime ago.
I don’t remember from when it didn’t work.
Anyway it is not a big problem, though.
Best regards,
Dalyoung