In which sentence does the underlined adverb clause modify an adverb?

three men crossed the atlantic ocean (in the double eagle ii) in 1978.
the double eagle ii was a hot-air balloon that flew farther (than other hot-air balloons.)
some balloonists who had tried to cross the atlantic ocean disappeared (before they were able to land).
(when the double eagle ii landed in paris), other balloonists who had planned to cross the atlantic cancelled their trip.

The sentence in which the adverbial clause modifies an adverb is 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. 

Some cultural backgrounds have different superstitions or customs, this can play a part in how they decide things. superstitions are important to a culture for example, an asian culture has a superstition about women putting their purses on the ground their money will be gone, therefore people in that culture try everything they can to not let their purse touch the ground in fear of it being true. also like how we avoid walking under ladders in fear of bad luck. customs may also play a key role a custom also know as a tradition, is something people in the culture have been doing for generations as a quick example, if a family has a necklace that the family's mother passes it on to her daughter in so on it's a custom in that family.