因为如果修饰radio就变成限定修饰,让人以为有很多种radio,而其中有一种是可以代替电话。整个句子变很怪: M认为"那种可以代替电话的radio"是一种私人对话的工具;instead,it("那种可以代替电话的radio") has become precisely..... 这样解会不会扯太远了??
"conceive of x as y" is the right form, so D and E are out (see below). from the context, the use of "a tool ..." is confusing in A and B - it looks like a definer of Radio, but closely follows telephone.