_____twice, the postman refused to deliver our letters unless we chained our dog.

_____twice, the postman refused to deliver our letters unless we chained our dog.

_____twice, the postman refused to deliver our letters unless we chained our dog.

_____twice, the postman refused to deliver our letters unless we chained our dog.

     twice, the postman refused to deliver our letters unless we chained our dog.

       A．Being bitten        B．Bitten                 C．Having bitten       D．To be bitten