Which of the Following Is True About the Structure of the Microtubule

Which of the following is true about the structure of the microtubule wall?

A) α-β-tubulin heterodimers are arranged with mixed orientation in each protofilament,and protofilaments are arranged with mixed polarity in the microtubule wall.
B) α-β-tubulin heterodimers are arranged with the same orientation in each protofilament,and protofilaments are arranged with mixed polarity in the microtubule wall.
C) α-β-tubulin heterodimers are arranged with the mixed orientation in each protofilament,and protofilaments are arranged with same polarity in the microtubule wall.
D) α-β-tubulin heterodimers are arranged with the same orientation in each protofilament,and protofilaments are arranged with same polarity in the microtubule wall.
E) Orientation of the α-β-tubulin heterodimers is completely random and depends on which end of the dimer first hits the end of the microtubule when it assembles.