Final answer:
Primary cilia are sensory and have a 9+0 structural arrangement, indicating the answer is D) sensory; 9+0.
Step-by-step explanation:
Primary cilia have a sensory function and typically display a 9+0 structure. Unlike their motile counterparts which display a "9 + 2 array" consisting of a ring of nine microtubule doublets with a central pair, primary cilia are involved in signal transduction rather than movement. Sensory cilia, which are typically found as one per cell, lack the central pair of microtubules, hence the 9+0 structure.