[单选题]
A string of mass m and rgh +,bidjo)b +vk eqvs nyp;-n +-)q5lengt p /prd+vsq a1b7p1w1ih L is under tension T. The speed of a wave in the string is v. What will be the speed of a wave in the string if thedrp v1pi1 7q1a+spbw/ length is increased to 2L, with no change in mass?
A. $0.5 \; v$
B. $0.71 \; v$
C. $1.4 \; v$
D. $2 \; v$