the experts were now fully convinced that the animal ___a puma

题目

the experts were now fully convinced that the animal ___a puma
1 must be 2 should have been 3 can only be 4 could only have been
请问选择哪一个,及分别说出每个为什么对与错
课文里面有一句话
The experts were fully convinced that the animal was a puma(这是课文原文)

答案

1 答案有问题.对过去事情的猜测,在表达“过去”事情时,如果强调“肯定是,一定是”的时候,应该用“must have been - - - - ”.
2 再说,句子裏面有了convinced,从句部分就不应该再用“must -- - - ”这样的结构.
3 这套练习题出得不好.