— Why do you look so worried?

— My computer broke down and my essay _____ since. [ ]

A. has been left unfinished

B. has left to finish

C. was left to finish

D. had been left unfinished

联合国世界旅游组织预测，到2020年，中国将成为世界第一大入境旅游接待国和世界第四大出境旅游客源国。