新概念3第一课书后几道习题不懂?1.Pumasneverattackahumanbeingexcept（D）corneredAtheyareBbeingCthattheyareDwhentheyare为什么不能选B?2.Theexpertswerenowfullyconvincedthattheanimal(D)apumaAmustbeB

Question

新概念3第一课书后几道习题不懂?
1.Pumas never attack a human being except （ D ）cornered
A they are B being C that they are D when they are
为什么不能选B?
2.The experts were now fully convinced that the animal(D )a puma
A must be B should have been C can only be D could only have been
为什么不能选A?
3.A private collector is a man who collects ( A ）.
A for his own benefit B on his own C in private D unknown to the public
为什么不选D?

Answer 1

except 有两种常用法：except for +名词,代词或V-ing,还有except + 从句 这句话是一种一般情况下的真理,而不是正在进行的动作.
fully convinced 已经表明十分确信了,A只是程度浅一些,只有D更符合那种肯定的语气.再加上因为主句为过去时态,则从句中的判断和推测要用could have done
要注意：这种题目属于选择最佳答案!
unknown形容词不能作为collect的宾语,如果为the unknown还勉强 起码无语法错误.