Ignore the first sentence about Defense Department. Simplify the question t why m industry use national security as an excuse in petition for import quotas. Then you'll find only C is the answer.
OG gives us a hint by saying: it is suprise that m industry raise national security,an issue seems have nothing to do with m industry, in its petition.
我是不明白og对A的解释,A. When the aircraft industries retooled, they provided a large amount of work for too builders. A explains why the industry might NOT raise the security issue, since it suggests that it might have raised the issue of jobs instead. retooled和security issue,有什么关系,句子中的两个it所指一样吗?