700+ Question

With stuff like this, I usually treat it like a real life issue that I would critique. For example: Immediately after reading the article, I asked myself, "So what if there are foreign workers inside the domestic companies?" So of course it is 'E' because the argument assumes that domestic companies only employ domestic workers. Although 'A' makes sense, the heart of the article is that the President wants to keep foreign workers away from military secrets, not the qualifications of the companies.

Assumptions are usually unstated premises.
Premise: Country M's domestic contractors are getting the defense contracts.
Conclusion: Job opportunities will improve. Option E links the two providing an unstated assumption that Domestic workers are among the workers working for domestic contracts. Since domestic contractors are awarded with the contracts they increase the job opportunity.

Option A is wrong as contractors ability is not the underlying assumption for increase in job opportunities.
All the other options doesn't affect the conclusion directly.