Each centriole is built as a cylinder of which arrangement of microtubules?

1. A centrosome is a microtubule-organizing center found near the nuclei of animal cells. 2. It contains a pair of centrioles that lie perpendicular to each other. 3. Each centriole is a cylinder built from nine triplets of microtubules. 4. Nine doublets around a central doublet describes the 9 plus 2 array of a flagellum or cilium instead, so that answer belongs to a different structure. 5. Nontubulin proteins hold the triplets of a centriole together. 6. The centriole arrangement is nine triplets. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 4 "Cell Structure", section 4.3 Eukaryotic Cells_