几个英语语言学考研问题，请根据语言学依据用英语帮助俺回答

1
distinctive features are features that help distinguish speech sounds.for instance,the voice [b] has distinctive features such as voiced and unaspirated.the former helps dintinguish [b] from [p],and the latter helps [b] differ from [ph].
2
speech sounds are infinite in languages because all the elements that make up the voice are changing all the time.e.g.,the openess of [a] varies every time the same speaker pronunces it.nontheless,the phonemes of a language are finite.
3
this is because words are finite in a language but sentences are not.and with words and grammar rules,sentences can be deduced.so there is no way and no need to make dictionary of sentences.

1
distinctive features are features that help distinguish speech sounds.for instance,the voice [b] has distinctive features such as voiced and unaspirated.the former helps dintinguish [b] from [p],and the latter helps [b] differ from [ph].
2