问题补充：
The Titanic, the biggest ship of its day, unsinkable, but it sank on its first voyage in 1912.
A. thought
B. was thought
C. thought it
D. was thought it
答案：
A. thought
(答案→)B. was thought
C. thought it
D. was thought it
解析：thought unsinkable 等于which was thought unsinkable. 在句中做非限制性定语
