Steffi and Ty Agree in an Exchange of E-Mail to Form

Steffi and Ty agree in an exchange of e-mail to form a partnership to deal in transfers of real property.Their partnership agreement is legally binding 

A)  ​only if a copy of the agreement is filed in the appropriate state office. 
B)  ​only if the agreement is put in writing on paper and signed by the parties. 
C)  ​only if the parties exchange valid consideration. 
D)  ​without more.