There were some children in the north looking at the swallows flying south. “Why are they going away?” the little one asked.

“The summer is over,” the elder sister answered, “and if they stayed here they would be starved and die of cold, and so, when the summer goes, they journey south.”

“Our mother and sisters are in the south,” the little one said, as they looked after the birds. “Dear little swallows, tell mother that we are watching for her!”

But they were already flying over the sea. The chilly winds tried to follow, but the swallows flew so swiftly they were not overtaken; they went on, with the summer always before them. They were tired many a time; once they stayed to rest upon the French coast, and once, in the Bay of Biscay, they clung to the rigging of a ship all through the night, but in the morning they went on again.

Far away in the south, two English children were looking from the turret window of an old castle.

“Here are the swallows,” they said; “perhaps they have come from England. Dear swallows, have you brought us a message?” they asked.

“It was very cold, we had no time for messages; and we must not lose the track of summer,” the swallows twittered, and they flew on till they reached the African shore.

“Poor little swallows,” said the English children, as they watched the ship come into port that was to take them back to their own land; “they have to chase the summer and the sun, but we do not mind whether it is summer or winter, for if we only keep our hearts warm, the rest does not matter.”

“It is very good of the swallows to come to us,” the elder sister said, in the next spring, when she heard their first soft twitter beneath the eaves, “for the summer is in many places, and we are so far from the south.”

“Yes, it is very good of them to come,” the children answered; “dear little swallows, perhaps they love us!”

What is a central idea of the passage?

A Persistence does not always pay off.

B Children are naturally curious.

C Surroundings can shape one's thoughts and opinions.

D People are capable of creating their own happiness.