参考修改:
Exactly, Aleko explained he had just bought a lamb, but it was black.
Dimitri was ashamed of his precipitance and he apologized to Aleko.
When they were talking, it started to rain.
So Dimitri went into Aleko’s house and stayed there until the rain stopped.
After half an hour, he went out, and he surprisedly found that the black lamb had changed to be a white one.
In fact, the stained wool was washed by rain