To begin with, I eliminated option B, as it is little unrelated(argument is not worried about the solution giver) to Engineer's argument. I could fish out option E and C (with little more thinking) as both cannot be the principles on which Engineer's argument be premised.
One might think Option D seems right, It is not the absence of discouragement in technical fixes to issue, But the feeling of more secure or sure about something (one might think that speeding is doable when roads are having less traffic, right?) So in a way this false sense of "doable/manageable" unknowingly encourages one to take risks.
GmatStuck
Engineer: Wide roads free of obstructions have been shown to encourage drivers to take more risks. Likewise, a technical fix to slow or reverse global warming by blocking out a portion of the sun’s rays would encourage more carbon dioxide emissions, which might cause more global warming in the future.
The engineer’s argument can most reasonably be interpreted as invoking which one of the following principles?
(A) Conditions that create a feeling of security also encourage risk taking.
(B) Problems created by humans require human-created solutions.
(C) Technical fixes are inevitably temporary.
(D) Technical fixes cannot discourage risk-taking behavior.
(E) The longer a problem goes unresolved, the worse it becomes.