9.After your analysis, you find that it is not practical to analyze the phenomenon in the
frequency domain in the continuous time. Afterward, you decide to use Discrete Fourier Transform
(DFT) instead. Assume you sample the new created r(x) signal every 2 unit time and collect 4 data
from time zero (ie., x are 0, 2, 4, and 6 sequentially.) If you know that the DFT can be formulated as

where the L is the length of the samples and the n indicates the sample number. Please select the right
following result of your analysis in the frequency domain after applying your derived DFT.
(A) ；
(B) ；
(C)；
(D)；