肯定句变否定句专项训练如下：
肯定句：She is a doctor.
否定句：She is not a doctor.
肯定句：They have finished their homework.
否定句：They have not finished their homework.
肯定句：He likes to play the piano.
否定句：He does not like to play the piano.
肯定句：I am going to the party.
否定句：I am not going to the party.
肯定句：We will meet at the cafe.
否定句：We will not meet at the cafe.
肯定句：She can swim very well.
否定句：She cannot swim very well.
肯定句：They enjoy watching movies.
否定句：They do not enjoy watching movies.
肯定句：He has visited Paris before.
否定句：He has not visited Paris before.
肯定句：I want to buy that book.
否定句：I do not want to buy that book.
肯定句：We should listen to our parents.
否定句：We should not listen to our parents.
肯定句：She believes in ghosts.
否定句：She does not believe in ghosts.
肯定句：They were playing soccer in the park.
否定句：They were not playing soccer in the park.
肯定句：He knows how to speak Spanish.
否定句：He does not know how to speak Spanish.
肯定句：We have finished the project on time.
否定句：We have not finished the project on time.
肯定句：She is going to the concert tonight.
否定句：She is not going to the concert tonight.
肯定句：They always enjoy their summer vacation.
否定句：They do not always enjoy their summer vacation.
肯定句：He will bring his laptop to the meeting.
否定句：He will not bring his laptop to the meeting.
肯定句：I have met him before.
否定句：I have not met him before.
肯定句：She sings beautifully.
否定句：She does not sing beautifully.
肯定句：They are going to invite us to the party.
否定句：They are not going to invite us to the party.
通过以上的专项训练，你可以逐步掌握肯定句变否定句的转换规则。这种练习有助于提高你对英语语法的理解和运用能力，帮助你在日常交流中更加灵活自如地使用不同类型的句子结构。