pp2-20&27

20. The courseof the Missouri River marks the ___ of continental glaciation.

a. approximate southern limit

c. southern limit and approximately

答案是a, 但我怎么觉得c也对,不是说副词后可以接介词短语吗?

27.While the term "hamony" suggests a pleasant or agreeable sound, it is aplied to any combination of notes, ___consonat or dissonant.

a. which

b.such

c.neither

d.whether

答案是D, whether但我听"王海波"语法中说whether 后接现在分词的时候有省略形式,过去分词前不能省略,怎么在这里可以呢?

20，C选项加上后怎么翻译？无法理解

27. 哪个是过去分词？