[单选题]
When the mass of a simple pendulum is tripler xg48p)ksn 2gctf9j zsm,,/qd, thevtfyb2jij0 ,:w1 g -lu time required for one complete vibration0j2bflgiwy:u t, j1-v
A. increases by a factor of 3.
B. does not change.
C. decreases to one-third of its original value.
D. decreases to 1/3 of its original value.