单选题：第二篇 A Desert Between Paul and Clara　　Paul had long promised

　第二篇 A Desert Between Paul and Clara
　　Paul had long promised to marry Clara. But at thirty-three he met and married Alice. Clara was driven mad.
　　Paul was taken to court. The judge ordered him to pay Clara $600 because of the broken promise. Paul had to borrow the money from a moneylender. He agreed to pay back $5 a month--for twenty years. His wages at the time were $16 a month.
　　Paul and Alice were poor but not unhappy. They had little enough food, certainly, even before the children began to-arrive. Each month Paul paid $5 to the moneylender.
　　He worked hard, never taking a holiday. In time, there were seven mouths to feed.
　　Illness was always with them. It grew serious when the oldest child was eight. The years of hunger weakened the family, because each month Paul paid $5. The details of the sickness were ugly, but the result was this: after twelve years of family life, Paul was alone in the world.
　　He lived alone, except for memories. Work was not now a god for him: it was a　pain-killer. Each month he paid, and in time the twenty years ended. From that moment　his wages were his own.
　　One day, it was a holiday-he went to the seaside. He sat down on a seat by the　sea. A middle-aged woman came and sat down near him. They recognized each other　at once.
　　The woman said, "The $600 has been in the bank since the day it was paid to me. It is now $6,000, and I have kept it for you. Will you let me share it with you?"　"No," said Paul, gently. "Each thousand is a lost life in a desert between us. It can never bring any happiness."
Paul was ordered to pay Clara $600 because
A ．he had borrowed $600 from her.
B ．he had broken his word to marry her.
C． he had promised to give her $600.
D． he had spent a lot of her money.