refer to后加什么?

refer to后加什么? refer to 后加什么 refer to后接动词什么形式 refer to 什么意思? refer to有些什么用法? refer to please refer to attachment 什么意思 refer to 和look up 什么区别. please refer要加to还是不加? What does "it" refer to here?为什么要加to? to后加什么词 adhere to后加什么