Let a signal x(t) = 3 cos (10πt) + cos (30πt) is sampled at a rate of 20 samples / second and reconstructed using on ideal low pass filter having cut off frequency of 20 Hz. The frequencies present in the reconstructed signal is / are.

• A. 5 Hz and 15 Hz
• B. 5 Hz, 10 Hz and 15 Hz only
• C. 10 Hz and 15 Hz only
• D. 5 Hz only