About the structure "not only - but also"

[cabin]

Hi,
Will you teach me if the following sentence is correct?

In order to master English, it is necessary not only to have a knowledge of grammar and vocabulary but also the ability to use English for the purpose of actual communication.

The sentence above does not follow the parallel structure; it goes "not only to have but also the ability." Is it all right to omit the part "to have" in the last half of the sentence?
Or, should it be like
"it is necessary not only to have a knowledge of grammar and vocabulary but also to have the ability ---" ?
If so, doesn't repeating "to have" clumsy?
Or, can I say
"it is necessary to have not only a knowledge of grammear and vocabulary but also the ability ---" ?

I also want to know if it is all right to say "a knowledge of grammar and vocabulary."
I heard somewhere that when the uncountable noun 'knowledge' is accompanied with modifiers, it comes with the particle 'a/an,' but I am not sure.
Thank you.
CABIN :-?

 

[Raymott]

Hi,
Will you teach me if the following sentence is correct?

In order to master English, it is necessary not only to have a knowledge of grammar and vocabulary but also the ability to use English for the purpose of actual communication.

The sentence above does not follow the parallel structure; it goes "not only to have but also the ability." Is it all right to omit the part "to have" in the last half of the sentence?
No
Or, should it be like
"it is necessary not only to have a knowledge of grammar and vocabulary but also to have the ability ---" ?
If so, [STRIKE]doesn't[/STRIKE] isn't repeating "to have" clumsy?
Yes it is..
Or, can I say
"it is necessary to have not only a knowledge of grammear and vocabulary but also the ability ---" ?
Yes, that's the correct way to write it.
I also want to know if it is all right to say "a knowledge of grammar and vocabulary."
Yes it is.
I heard somewhere that when the uncountable noun 'knowledge' is accompanied with modifiers, it comes with the particle 'a/an,' but I am not sure.
Thank you.
CABIN :-?

I'm not sure what you mean in your last point. The noun 'knowledge' does come with an 'a' in this sentence, and it's correct.

 

[cabin]

Thank you Raymott for your simple answer.^^
CABIN