Task: Question Generation
Input (English):  The book tells the story of the quest for Captain Grant of the Britannia. After finding a bottle the captain had cast into the ocean after the Britannia is shipwrecked, Lord and Lady Glenarvan of Scotland contact Mary and Robert, the young daughter and son of Captain Grant, through an announcement in a newspaper. The government refuses to launch a rescue expedition, but Lord and Lady Glenarvan, moved by the children's condition, decide to do it by themselves. The main difficulty is that the coordinates of the wreckage are mostly erased, and only the latitude (37 degrees) is known; thus, the expedition would have to circumnavigate the 37th parallel south. The bottle was retrieved from a shark's stomach, so it is impossible to trace its origin by the currents. Remaining clues consist of a few words in three languages. They are re-interpreted several times throughout the novel to make various destinations seem likely.
Lord Glenarvan makes it his quest to find Grant; together with his wife, Grant's children and the crew of his yacht, the Duncan, they set off for South America. An unexpected passenger in the form of French geographer Jacques Paganel (he missed his steamer to India by accidentally boarding on the Duncan) joins the search. They explore Patagonia, Tristan da Cunha Island, Amsterdam Island, and Australia (a pretext to describe the flora, fauna, and geography of numerous places to the targeted audience).
There, they find a former quarter-master of the Britannia, Ayrton, who proposes to lead them to the site of the wreckage. However, Ayrton is a traitor, who was not present during the loss of the Britannia, but was abandoned in Australia after a failed attempt to seize control of the ship to practice piracy. He tries to take control of the Duncan, but by sheer luck, this attempt also fails. However the Glenarvans, the Grant children, Paganel and some sailors are left in Australia, and mistakenly believing that the Duncan is lost, they sail to Auckland, New Zealand, from where they want to come back to Europe. When their ship is wrecked south of Auckland on the New Zealand coast, they are captured by a M ori tribe, but luckily manage to escape and board a ship that they discover, to their astonishment, to be the Duncan.
Ayrton, made a prisoner, offers to trade his knowledge of Captain Grant in exchange for being abandoned on a desert island instead of being surrendered to the British authorities. The Duncan sets sail for the Tabor Island, which, by sheer luck, turns out to be Captain Grant's shelter. They leave Ayrton in his place to live among the beasts and regain his humanity.
Ayrton reappears in Verne's later novel, L' le myst rieuse (The Mysterious Island, 1874).
Output (English): What is the main difficulty in rescuing the Britannia?