Engines,
Thoughtful and right to a point...
But..
The F-35A and F-35C have this huge hole just behind the cockpit, which is nice to some extent for extra fuel but is not in the right place...
The F-35A and F-35B have two more tails (at least) than they need...
The F-35B has an internal weapons bay (which it won't need all that much) and no internal gun (which arguably it will need)...
And single engine does not necessarily mean cheap.