The question is as follows:

An interfering signal from a transmitter is found to have a frequency of 57 MHz (TV Channel 2 is 54 - 60 MHz). This signal could be the:

And the options are as follows:

A) crystal oscillator operating on its fundamental
B) second harmonic of a 10 metre transmission
C) seventh harmonic of an 80 metre transmission
D) third harmonic of a 15 metre transmission

Now in my mind options B and D are the same frequency as the second harmonic of a 10 meter transmission is 30hz2=60hz and the third harmonic of a 15meter transmission should be 20hz3=60hz. I don’t see how One answer could be more correct than the other.