White cumulus marched away through the blue to the pale southeastward rim of the world, but the sun kept its warm blaze against us, partly drying our wet skin. In the thin air the white vapor of our breathing took shape.

"Colder than you'd think," John said.

请问老师红色部分为什么要用虚拟语气，可不可以用 you think 或 you thought？