My sister is determinedshe has made up her mind nothing can change it. A. ThoughB. On

问题补充：

My sister is determined. she has made up her mind, nothing can change it.

A. Though

B. Once

C. Unless

D. Until

答案：

A. Though

(答案→)B. Once

C. Unless

D. Until

解析：“一旦”下定决心，什么也不能改变（她的决心）。once: as soon as, when, 引导时间状语。A项引导让步状语从句；C项引导条件状语从句；D项引导时间状语从句，但是要求主句动词为延续性动词或动词的否定形式。故B项正确。