[单选题]
The third harmonic oqcp :k/fn-7q2vwpp/y us 8ip- f a complex ton)d8 ijv 9 kys gjpkebr6x2nog556*v66- yqn ike has a frequency of 1200 Hz. What is the frequency of the gb8nkyix* d q5-6vkn6p9g6)25jso ji vkry6efourth harmonic?
A. $400 \; Hz$
B. $900 \; Hz$
C. $1600 \; Hz$
D. $4800 \; Hz$
