请你观察下面的词组。注意词组中“a”和“an”的用法有何区别。

a book　　a bag　　a pencil

a photo　　an eraser　　an apple

a和an的用法区别：________________________

请你根据以下例句，总结出play、come、have to、study和visit的用法结构。

　　play:

　　1)The children are playing with a ball.

　　2)Do you want to play football this weekend?

　　3)He is playing the piano.

　　4)They are watching a TV play.

　　________________________________

　　come:

　　1)How do you come to school?

　　2)Do you want to come to my birthday party?

　　3)Marie's birthday is coming soon.

　　4)Monday comes after Sunday.

　　________________________________

　　have to:

　　1)Does Dave have to do his homework now?

　　2)I can't join you because I have to help my mom.

　　3)Mary has to stay at home because her mother is ill.

　　4)He doesn't have to go there.

　　________________________________

　　study:

　　1)Does Rosie study English?

　　2)Please keep quiet t I'm trying to study.

　　3)She is studying the map.

　　4)Tom studies very hard.

　　________________________________

　　visit:

　　1)The students are visiting Uncle's factory.

　　2)My American friends are going to visit me next vacation.

　　3)They are on a visit to Shanghai.

　　4)Thank you for your invitation to visit next week.

　　________________________________