Paragraphs 5-6 of the passage mainly add to the development of the text by showing that Mafatu is afraid to go out into the ocean with the others. The correct answer is option D.
Paragraphs 5-6 of the passage mainly add to the development of the text by showing that Mafatu is afraid to go out into the ocean with the others. This is indicated by the description of Mafatu's physical reaction - his knuckles whitening and his ears pounding with the swift fury of the sea.
This passage suggests that Mafatu has a fear or anxiety about going out into the ocean, which is why his knuckles whiten and his ears pound with the sound of the sea. It implies that he may not feel comfortable or confident enough to join the other boys in their fishing expedition.
The passage does not provide information about the difficulty of catching bonitos, Mafatu being jealous of the other boys, or the loud sound of the sea hurting Mafatu's ears. Therefore, answer choices A, B, and C are not supported by the text.
In conclusion, the main development in paragraphs 5-6 is that Mafatu is afraid to go out into the ocean with the others, as evidenced by his physical reactions and the mention of his fear in the passage.
Therefore the correct answer is option D.