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”