问题补充：
动词不定式肯定形式和否定形式
答案：
以下是动词不定式肯定形式和否定形式的例句：
(1) 三个动词不定式肯定
To work out this difficult problem in three days is impossible
=It is impossible to work out this difficult problem in three days
To learn English so well is of great importance to us all
=It is of great importance to us all to learn English so well i
To swim across the river is very easy for the little boy
=It is very easy for the little boy to swim across the river
(1) 三个动词不定式否定
Our teacher often tells us not to be late for school
His parents want him not to play with those bad boys
The girls are told not to go out alone in the evening /at night
