A)2 central microtubules ringed by 9 microtubule doublets B)2 central microtubule doublets ringed by 9 microtubules C)9 central microtubules with 2 microtubules attached to each central microtubule D)9 central microtubules with 2 microtubule doublets attached to each central microtubule E)none of the above