[单选题]
A string of mass m and length L is undefp + x9k;zu1chr tension T. The speed of a waotgosu8 k6f;kw 8u2nz/ :qf j+ve in the string is v. What will be the speed of a wave in the string if the tek w/zk6gs8ou f+oj;ftuq28n :nsion is increased to 2T?
A. $0.5 \; T$
B. $0.71 \; T$
C. $1.4 \; T$
D. $2 \; T$