In which sentence does the underlined adverb clause modify an adverb?
1. When the Double Eagle II landed in Paris, other balloonists who had planned to cross the Atlantic cancelled their trip.
2. Three men crossed the Atlantic Ocean in the Double Eagle II in 1978.
3. Some balloonists who had tried to cross the Atlantic Ocean disappeared before they were able to land.
4. The Double Eagle II was a hot-air balloon that flew farther than other hot-air balloons.
The adverb it modifies is "farther".
All of the other sentences have clauses that modify verbs, not adverbs.
