[单选题]
A string of mass m and length 9 e4zbdyo(2 tgL is under tension T. The *d4dy rh 3xa+gspeed of a wave in the string is v. What will be the speed of a wave a*ygr3 4+hxd din the string if the length is increased to 2L, with no change in mass?
A. $0.5 \; v$
B. $0.71 \; v$
C. $1.4 \; v$
D. $2 \; v$