[单选题]
A wave moves on a string wih9rn8o8 5 cvmfth wavelength l and frequency f. A second wave on the-j:u-ab3d p ee same string has wavelength 2l and travels with the same velocbeead-3u:j -pity. What is the frequency of the second wave?
A. $0.5 \; f$
B. $f$
C. $2 \; f$
D. It cannot be determined from the information given.
