集体合同是（）。

A.约定要式合同

B.非要式合同

C.法定要式合同

D.口头合同，

— Excuse me, I want to have a letter mailed, but I can't find a post office.   

—  I know ______ nearby. Come on, I'll show you. [      ]

A. it          

B. one          

C. that        

D. another