Concept:The blank should explain why an elected leader receives criticism but no credit for infrastructure benefits.
Explanation:The passage says infrastructure costs are short-term but benefits are long-term.
The word "flak" means harsh criticism, which matches the leader's negative reception.
The sentence after the blank refers to an elected leader who gets blamed but not praised.
This makes sense only if the leader who approves the project is different from the one who inaugurates it later.
So the approving politician faces the short-term costs and criticism, while the later politician enjoys the praise.
The other options discuss private investors, externalities, or poor returns, none of which connect to the leader's situation.
Answer:Option B: "The politician that authorises the project is rarely the same one that opens it."