A doctor was teaching some medical students at a famous hospital. A patient was brought in, and the doctor asked one of his students, "What's wrong with this man?" "I don't know, sir," the student answered. "I need to examine him." "There's no need to examine him," said the doctor. "You should know without asking questions. He has hurt his right knee. Didn't you notice the way he walked? He hurt it by burning it in the fire. You see his trousers leg is burnt away at the knee. This is Monday morning. Yesterday was fine, but on Saturday the roads were wet and muddy. The man's trousers are dirty all over. The man fell down on Saturday night." The doctor then turned to the man, "You had your pay on Saturday and went to a public house and drank too much. You got muddy and wet on the way home. Because you had drunk too much, you fell on the fire and burnt your knee. Is that right? "Yes, sir," said the man. The man hurt his knee    _  .
on Monday on Sunday night on Saturday night yesterday