Which of the following conditions will make a relation that is in first normal form to be in second normal form　　Ⅰ. every non-key attribute is functionally dependent on the full set of primary key attributes.　　Ⅱ. no non-key attributes exist in the relation.　　Ⅲ. the primary key consists of only one attribute.

A．Ⅰ only

B．Ⅰ and Ⅱ only

C．Ⅰ and Ⅲ only

D．any of them