Correct Option (B)
The passage explicitly states, "After we had travelled for about twenty kilometers, there was still no sign of the town which was marked on the map. We were beginning to get worried." The map indicated the town was approximately fifteen kilometers away. Therefore, having traveled five kilometers beyond the expected distance without reaching the town, the travellers' worry is directly attributable to the probability of having lost their way, as the expected landmark was absent.
Incorrect Options:
- Option 1: While the setting was a remote countryside, the passage does not identify this as the specific cause of worry at the twenty-kilometer mark. The concern is linked to the absence of the town.
- Option 3: The rain began earlier, as they climbed higher, before reaching the twenty-kilometer point. While it contributed to difficult driving conditions, it is not presented as the direct reason for their worry specifically after travelling twenty kilometers and not finding the town.
- Option 4: The increasing coldness is mentioned as they drove higher, preceding the twenty-kilometer mark. This describes an environmental condition but is not cited as the cause of their anxiety when the town failed to appear.