My flat is twice bigger than Tom's.(同义句转换） My flat is three times ____ ____ ____ Tom's.

同义句
My flat is three times as big as Tom's.能解释一下原因吗原句My flat is twice bigger than Tom's.我的公寓比汤姆的（公寓）大两倍。同义句就是：My flat is three times as big as Tom's. 我的公寓是汤姆的（公寓）的三倍（大）as big as .... 和。。。一样大three times as big as ... 和。。。的三倍一样大。