Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions.

Opononi, New Zealand, was a quiet little town by the sea. Most of the men worked as fishermen. In the summer of 1955, they noticed that a strange sea animal was following their boats. At first the men thought it must be a shark. But the animal came closer and closer to the boats. Before long everyone could see it was a dolphin. One of the fishermen named her Opo - after the town.

At first, Opo was shy, as many wild dolphins are. But she was curious, too. Every day she swam closer to the boats. Finally one of the fishermen reached out as far as he could with his oar. He scratched Opo with it.

She reared back in the water. But the oar must have felt good, for soon Opo came closer than ever before. Then she rolled over. The men had to laugh. Opo was plainly saying, "Scratch my belly this time."

A scientist came to look at Opo. He said Opo was a young dolphin who had probably lost her mother. That was why she was swimming alone. Opo might have been an orphan, but she soon found a new family. The whole town of Opononi adopted the friendly dolphin.

When the men first noticed something in the water, they thought it was a _______. A. boat B. shark C. dolphin D. swimmer