Bases in Battlegroup

[nicofig]

Hi,
I find that the rules are very well written, but I am not english and I does not understand perfectly the following paragraph :

"Each BG must initially comprise an even number of bases."

Does that mean that all my BG must, for example, have 4 bases that it is cavalry or infantry? Can I have my infantry with 6 bases ( all infantry or just for the same type) and my Cavalry with 3 bases ( all cavalry or just for the same type) for exemple ?

and after :

'The only exception to this rule is that BG, whose official army list specifies them as 2/3 of one type and 1/3 of another, can comprise 9 bases if this is within the battle group size range specified by their list".

You have an example ?

I play a little the ingenuous one but I try to read the rules as if I were a complete beginner to point the difficulties of comprehension .
Thank you very much

[hammy]

Battle groups can only be bought as 2,4,6,8,9,10 or 12 bases. 9 is a special case that requires 2/3 one type and 1/3 another.

I think it is clear in english but may need careful translation.

[nicofig]

Exact. It's why I asked this question