> A. These kind<strong>s</strong> of problem are to be avoided.
>
> B. These kind of problem<strong>s</strong> are to be avoided.

Are both A and B grammatical? If not, why not? If so, after having noticed the parallelism between A and C, and between B and D, could we say that C and D are "standard" English, too? 

> C. These kind<strong>s</strong> of problem are ones to avoid.
>
> D. These kind of problem<strong>s</strong> are ones to avoid.