there is a formula that involves integration to find the fourier series of a function. it is a series that represents signals by an infinite sum of sines and cosines (it can be finite, but it is still an infinite sum with amplitudes equal to zero). The sines represent the odd parts of a function (sensible considering sine is odd) and cosines represents the even parts of a function (again, sensible). A third conceptual rule is that the non-sinusoidal component, often called the DC-component, represents the average value of the signal over the range that the fourier series represents (and is a cosine with a frequency of zero + is even)

You can eliminate many possibilities by using these three rules. First off, this function is even. Therefore, (b), since it has a sinewave, is wrong. Also, since this function never goes negative, it has an average value. This makes (c) wrong.

you can find the equation here. Fourier Sine and Cosine Series

I assume there may be another little trick you can use to eliminate one of the last two possibilities. However, I do not know it. You may just have to suffer the integration.