—Now that you like the personal computer very much, isn’t it

—Now that you like the personal computer very much, isn’t it a good idea to get one?
—Well, I’d like to but I can’t afford ___ computer at present.
A. that expensive a B. a such cheap C. that an expensive D. so cheap
解释一下选项的句型
谢谢
选项的句型

A
that=so