Two Strings, One Thick (Linear Density 2 $\mu$ ) and the Other Thin (Linear Density

Two strings, one thick (linear density 2 $\mu$ ) and the other thin (linear density $\mu$ ) , are connected to form one long string. The speed of a wave traveling along the string and from the larger-linear density to the lower-linear density parts is

A) unchanged.
B) decreased by a factor of 2.
C) increased by a factor of 2.
D) decreased by a factor of $\sqrt { 2 }$
E) increased by a factor of $\sqrt { 2 }$