I am about the new model and I firmly believe that there will be a good market for it.

问题补充：

I am about the new model, and I firmly believe that there will be a good market for it.

A. concerned

B. doubtful

C. confident

D. particular

答案：

A. concerned

B. doubtful

(答案→)C. confident

D. particular

解析：

试题分析: 句意：我对新的样品很有信心，我坚定地相信它会有很好的市场。A be concerned about“关心，担心”；B be doubtful about “对……怀疑”；C be confident about “对……有信心的”；D be particular about “对……挑剔。从句意可知答案选C。