1.Draw a picture for his friend,Ann.
【讲解】祈使句的否定形式一般是在谓语动词前加上do not或don't（口语中）,有时也可用never.若祈使句有主语,否定词don't或never要置于主语之前.
Do not come in unless asked.非请莫入.
Don't you believe it.决不要相信它.
Never be late again next time.下一次千万不要再迟到了
2.How often should Koko werrp the stairs
【讲解】three times a week一周三次,问的是频率,用how often+一般疑问句