variants and charcteristics

I made produkt A with variants aa, bb, cc, etc
Then I make produkt B and give as an option > produkt A

When there is no variant in produkt A it goes ok > the option apears for selecting No (and adding no price) or produkt A with its price summed up.
When A has variants it also apears as an option to produkt B But there is no more option of NOT selecting this Option. So it ads up this option and cost anyway.

What can i do to make it work with variant but without forcing the option to the customer?

In your product with variants, you can create a new variant with the name "No" (for example) with no price.
By this way in the options listing, the option No will appear, and you can set this variant as the default one.