He was busy writing a story, only ______ once in a while to smoke a cigarette.

A. to stop                     B. stopping            C. to have stopped      D. having stopped

He was busy writing a story, only ______ once in a while to smoke a cigarette.

A. to stop                     B. stopping                          C. to have stopped  D. having stopped

He was busy writing a story, only ______ once in a while to smoke a cigarette.

A. to stop          B. stopping     C. to have stopped      D. having stopped

He was busy writing a story, only ______ once in a while to smoke a cigarette.

A.to stop                B.stopping                 C.to have stopped        D.having stopped

He was busy writing a story, only ______ once in a while to smoke a cigarette.

A. to stop                     B. stopping                          C. to have stopped  D. having stopped

He was busy writing a story, only _____once in a while to smoke a cigarette.

He was busy writing a story, only _____once in a while to smoke a cigarette.

A．to stop           B．stopping          C．to have stopped    D．having stopped

He was busy writing a story , only _______ once in a while to smoke a cigarette.

He was busy writing a story, only ____ once in a while to smoke a cigarette.

A. to stop      B stopping      C to have stopped      D having stopped

He was busy writing a story, only ______ once in a while to smoke a cigarette.