庭丰说的完全正确 thank you !

作升调处理时, 句子本身貌似祈使句,但他们是问句(yes and no questions)的简写.

Shut the door -> Will you shut the door?
Bring me a chair -> Can you bring me a chair?
Sit down -> Would you like to sit down?  
Have a try -> Will you (can you) have a try? 
Open the window -> Shall I open the window? or Will you open the window?