If two tones $$f_1$$ and $$f_2$$ are amplified by a non-linear amplifier, which frequency components would be present in output?

A

$$f_1, f_2$$

B

$$f_1, f_2, f_1 + f_2, f_1 - f_2$$

C

$$f_1 + f_2, f_1 - f_2$$

D

$$nf_1 \pm mf_2$$, where n and m are integers