Hi. The answer of this question is (d) - the Germans had destroyed their home.
From the story:
She was eager to do so. They were, she explained, quite alone in the world, except for
this sister, Lucia. Their father, a widower, a well-known singer, had been killed in the
early part of the war. Shortly afterward a bomb had destroyed their home and thrown the
three children into the streets. They had always known a comfortable and cultured life --
- Lucia had herself been training as a singer --- and they had suffered horribly from near
starvation and exposure to the cold winter.
For months they had barely kept themselves alive in a sort of shelter they built with their
own hands amidst the rubble. Then for three years the Germans ruled the city. The boys
grew to hate the Germans. When the resistance movement began secretly to form they
were among the first to join. When the war was over, and we had peace at last, they
came back to their beloved sister. And they found her..... suffering from tuberculosis of