C. Sailors opened the shark's belly because... 1. They were hungry. 2. They hoped to find something interesting. 3. They wanted to know the biology of the shark. 4. They thought that the shark was pregnant.

Обоснование: В тексте сказано: "Suddenly, a sailor saw a large fish in the water. It was a shark. Captain Mangles gave orders, and the fishin caught the fish. But that wasn't all. All the sailors opened the shark's belly after the catch. They hoped to find som...". Далее текст обрывается, но ясно, что они открыли живот акулы, надеясь что-то найти. Во всех вариантах, кроме второго, нет логического продолжения этой мысли. Вариант "They hoped to find something interesting" наиболее точно соответствует началу предложения в тексте.

Ответ: 2. They hoped to find something interesting.