Although the airline industry is extremely competitive, Southwest Airlines$$ turns a profit virtually every year. One key reason why is a legendary organizational culture that inspires employees to do their very best.$\text{'}---$ This is associated with what strategic resource characteristic according to course reading $($not necessarily from the textbook$)?$

A$.$

Marketing mix

B$.$

Difficult$-$to$-$immitate

C$.$

Non substitutable

D$.$

Rare

E$.$

Valuable