What he bought you when he came to see you yesterday? A. is

What he bought you when he came to see you yesterday? A. is it B. is that C. was it D. was it that
Whatheboughtyouwhenhecametoseeyou yesterday?
A. is it B. is that C. was it D. was it that
为什么选D
当关系代词that在定语从句中用作动词宾语或介词位于句末时的介词宾语时,可以省略.为什么这里不能省略