Our ______ sensitivity decreases with age. By age 60, most people have lost 40 percent of their ability to smell and 50 percent of their taste buds.

A．although
B．as
C．but
D．while

A．In the early to mid 18th century.
B．In the early to mid 19th century.
C．In the early 19th century.
D．In the early 18th century.