[求助]GWD-TN-21 37句子结构

37. GWD31-37

In 1994 the white house named Dr RuthR. Faden chairperson of the federal advisory committee of experts they assigned to do a report on the history and ethics of the government’s radiation experiments on humans in the 1950’s and 1960’s .

A.          they assigned to do

B.          to be assigned doing

C.          that was being assigned doing

D.         assigned for doing

E.          it assigned to do

答案是E

想来想去想不明白 我想知道划线部分是干嘛的

我的想法本来是NAMED...to 选的B 错了

请大虾指教

划线部分想表达的意思是“这些专家的任务是撰写关于……的报告”。
A项的they无法指代the white house。
B项的assign doing不符合assign的用法。
C项也是assign的用法不对，而且用过去进行时时态无法解释。
D项assign的用法不对。
E项正确，it可以指代主语the white house，而且assign to do正确。该划线部分可以看作...the federal advisory committee of experts (that) it assigned to do a report.即白宫指派这些专家做一个报告。