If you don't know how to spell new words , ______ in the dictionary.       [ ]

A. look up them    

B. look for them    

C. look them up      

D. look them for

小张因购房向其友人借款数万元，双方就利息未有约定，则此合同性质为( )。

A．要物合同

B．有偿合同

C．诺成合同

D．无名合同