Solution: Choice B is correct

This question is based on the concept of parallel structure

A) “To appreciate” doesn’t match the structure of other list items: “knowledge” and “courage”

B) “An appreciation of” matches the structure of other list items: “knowledge” and “courage” creating an appropriate parallel list.

C) “Appreciating” doesn’t match the structure of other list items: “knowledge” and “courage”

D) “They must appreciate” doesn’t match the structure of other list items: “knowledge” and “courage”