Technologically, it is already possible to produce nonpolluting cars that burn hydrogen rather than gasoline.
Conclusion
This infrastructure is likely to appear and grow rapidly. (i.e. The national system of fuel stations for hydrogen fuel is likely to appear and grow rapidly)
Evidence
It's already possible to produce nonpolluting hydrogen cars. And, a century ago there was no fuel infrastructure for gas powered vehicles, but it quickly developed in response to consumer demand.
Evaluation
When we're doing Conclusion questions, we're primarily expecting the conclusion to be the very first claim, or to appear after some sort of But / Yet / However pivot.
Here we get the latter form. There is a pivot with "but" that introduces a fact: this system of stations does not yet exist. Then there is a pivot with "however" that introduces an opinion: this infrastructure is likely to appear soon.
The author then supports that opinion with the historical comparison premise in her last sentence.
Goal
Just look for an answer that says .