The correct answer is range of knowledge.
D. range of knowledge
The correct answer is (D) Range of (one's) knowledge; (one's) knowledge or cognizance, mental perception, range of sight, or vision.
Ken comes from Middle English kennen (to make known), Old English cennan, Icelandic kenna, German kennen.
Examples of use:
- Austerity was a concept not in her ken.
- Complete understanding of the universe is beyond our ken.