●肯定结构:
Do型(即:动词原形(+宾语)+其它成分).如:Please have a seat here.请这边坐.
●否定结构:
Do型和Be型的否定式都是在句首加don't构成.如:Don't forget me!不要忘记我!
Don't be late for school!上学不要迟到!