If we want to EVALUATE an argument, we must first figure out where the argument is flawed: we must find a missing link between premises & conclusion.

Conclusion:
The drop in enrollment of foreign-born graduate students since 2001 will hurt America's competitiveness in basic research and applied technology, with serious consequences for years to come.

Reasoning:
- de-internationalization of graduate programs across the country will also negatively affect the global outlook and experience of the American students
- they will not have the opportunity to learn about foreign cultures directly from members of those cultures

Missing:
Just because students miss the opportunity to learn from foreign classmates, does that mean that they will miss ALL opportunities to learn from other cultures? Are there places outside of the classroom that they can meet these people? Can they travel abroad themselves?

We need to select an answer choice that asks a question about this missing information:

A. What is the cost to reverse the trend of insourcing in America?
Cost might be relevant to whether certain plans get enacted, but it wouldn't give us much information about whether the conclusion is valid - whether lack of insourcing really deprives American students of cultural experience.

B. How does insourcing replace domestic jobs lost from outsourcing?
Irrelevant - our argument is only about the impact on American students.

C. Since 2001, what has been the decrease in the number of foreign-born students in America?
We're told that there has been a decrease. Knowing the specific number wouldn't add anything that the argument is currently missing; it wouldn't help us to determine whether American students are disadvantaged.

D. What opportunities do American graduate students have to interact regularly with foreigners who are not students?
This directly addresses the missing piece in the argument. If the answer is "not much," then the thrust of the argument holds. If the answer is "a lot," then the argument about lack of insourcing hurting American students doesn't hold much weight.

E. What effect would a government policy have on the number of foreign graduate students?
This is similar to C: it would give us more information about something we already know. We're told that a government policy change would help. We don't need to know the exact specifics of that effect. It doesn't address what the argument is currently missing: opportunities outside of graduate school for American students to learn from foreign cultures.

The answer is D.