Find the correctly spelt words.

The correct answer is D. Rigorous.

The word “rigorous” means “strict, demanding, or severe.” It is derived from the Latin word “rigor,” which means “stiffness” or “harshness.” The word “rigorous” is often used to describe academic or physical challenges, as well as rules or regulations.

The other options are incorrect because they are not spelled correctly. The word “rigerous” is missing the “u” in the middle, the word “rigourous” has an extra “u” at the end, and the word “regerous” has an extra “e” at the beginning.