The math problem is so diffcult that I can't work out.The room is so small for us that we can't live in.The schoolbag is so expersive for me that I can't buy it.是三种同义句啊The math problem is not easy to work out.The math problem is such adiffcult problem that I can't work out.The room is not big enough for us to live in.The room is such asmall room for us to live in.The schoolbag is not cheap enough for me to buy .The schoolbag is such an expersive schoolbag for me that I can't buy it.