Final answer:
The core of a cilium is called the axoneme. Cilia are composed of microtubules organized in a specific arrangement. Hence the correct answer is option 4
Step-by-step explanation:
The core of a cilium is called the axoneme. Cilia are hair-like structures found on the surface of some eukaryotic cells, and they are composed of microtubules organized in a specific arrangement. The axoneme is the central part of the cilium that consists of doublet microtubules surrounded by singlet microtubules.
Hence the correct answer is option 4