Explanation:
Cyclic ethers are a type of organic compound containing an oxygen atom in a ring structure. For the molecular formula C4H8O, we can draw different cyclic ethers by considering different arrangements of the atoms in the ring.

1. Tetrahydrofuran (THF)
THF is a cyclic ether in which four carbon atoms and an oxygen atom are arranged in a ring. It is the most commonly used cyclic ether in organic synthesis.

2. Oxetane
Oxetane is a cyclic ether in which three carbon atoms and an oxygen atom are arranged in a ring. It is a strained molecule due to the angle strain in the ring, and is used as a synthetic intermediate.

3. 1,2-Dioxolane
1,2-Dioxolane is a cyclic ether in which two carbon atoms and two oxygen atoms are arranged in a ring. It is used as a solvent and as a reagent in organic synthesis.

4. 1,3-Dioxolane
1,3-Dioxolane is a cyclic ether in which three carbon atoms and two oxygen atoms are arranged in a ring. It is used as a solvent and as a reagent in organic synthesis.

5. 1,4-Dioxane
1,4-Dioxane is a cyclic ether in which four carbon atoms and two oxygen atoms are arranged in a ring. It is a common solvent for organic compounds.

6. 1,3-Dioxane
1,3-Dioxane is a cyclic ether in which three carbon atoms and two oxygen atoms are arranged in a ring. It is used as a solvent and as a reagent in organic synthesis.

Thus, there are six cyclic ethers excluding stereoisomers for the molecular formula C4H8O. The correct answer is option 'D'.