这道题我彻底的不明白。求教！

海角天涯

请问，为什么答案是C? 其他4个选项都哪里不对？这道题我彻底没有摸到头绪。

Defense Department analysts worry that the ability of the United States to wage a prolonged war would be seriously endangered if the machine-tool manufacturing base shrinks further.  Before the Defense Depaartment publicly connected this security issue with the import quota issue, however, the machine-tool industry raised the national security issue in its petition for import quotas.

Which of the follwoing, if true, contributes most to an explanation of the machine-tool industry's raising the issue above regarding national security?

(A) When the aircraft industries retooled, they provided a large amount of work for tool builders.
(B) The Defense Department is only marginally concerned with the effects of foreign competition on the machine-tool industry.
(C) The machine-tool industry encountered difficulty in obtaining governmental protection against imports on grounds other than defense.
(D) A few weapons important for defense consist of parts that do not require extensive machining.
(E) Several federal government programs have been designed which will enable domestic machine-tool manufacturing firms to compete successfully with foreign toolmakers.

lawyer_1

问题要你找一个能解释为何工具工业要将进口限额和国家安全联系起来。C说该行业在要求政府限制工具进口时，除了以国防为理由外，其他理由有困难。原文只是个背景，没有什麽推理。