Let A and B be two drawing pins such that AB=10 units .Consider a string whose end points are at A,B and length is of 16 units. If the point of pencil moves on paper such that fixed ends of string are always tight the area encolsed by curve traced by pencil is
A 36π sq. units
B 100π sq. units
C 16√39π sq. units
D 8√39π sq. units