A 9+2 arrangement of microtubules is observed in one of the following? 
A) Cilia  
B)  Eukaryotic flagella 
C)  Centrioles  
D)  Prokaryotic flagella 

Flagella are comparatively longer and responsible for cell movement. The prokaryotic bacteria also possess flagella but these are structurally different from that of the eukaryotic flagella.

Eukaryotic flagella : The electron microscopic study of a cilium or the flagellum show that they are covered with plasma membrane. Their core called the axoneme, possesses a number of microtubules running parallel to the long axis. 

The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. Such an arrangement of axonemal microtubules is referred to as the 9+2 array