Assume your uncle recorded his salary history during a $40-$year career and found that it had increased $10-$fold. If inflation averaged $4\%$ annually during the period, how would you describe his purchasing power, on average?

A$.$ His purchasing power remained the same.

B$.$ His purchasing power decreased by $1\%$ annually.

C$.$ He beat inflation by slightly below $2\%$ annually.

D$.$ He beat inflation by $5\%$ annually.