A、His friend gave him the wrong key. B、He didn’t know where the back door was. C、He couldn’t find the key to his mailbox. D、It w

My friend Vernon Davies kept birds. One day he phoned and told me he was going away for a week. He asked me to feed the birds for him and said that he would leave the key to his front door in my mailbox. Unfortunately, I forgot all about the birds until the night before Vernon was going to return. What was worse, it was already dark when I arrived at his house. (20)I soon found that the key Vernon gave me could not unlock either the front door or the back door. I was getting desperate. (21)I kept thinking of what Vernon would say when he came back. I was just going to give up when I noticed that one bedroom window was slightly open. I found a barrel and pushed it under the window. As the barrel was very heavy, I made a lot of noise. But in the end, I managed to climb up and open the window. (22)I actually had one leg inside the bedroom when I suddenly realized that someone was shining a torch up at me. I looked down and saw a policeman and an old lady, one of Vernon’s neighbors.
    "What are you doing up there?" said the policeman.
    Feeling like a complete fool, I replied, "I was just going to feed Mr. Davies’ birds."
20. Why couldn’t the man open the door?
21. Why did the man feel desperate?
22. Why did the man feel like a fool?