Discrete Fourier Transform in Signal Processing - Interpreting graphs of transformed signals
(iii) seems be to correct. Spectrum of two frequencies.

The other choices can be verified,

(i) Fourier transform of $f(t=0)=1$ is 1. So it cannot be graph (iii)

(ii) Signal (iii) is sine wave and there is no spectrum associated with that.

(iv) It's Fourier transform of sine wave (iii) which is

$$f(t)=0.5\cdot \sin(2\pi Ft)$$

and it's transform is

$$\frac{\pi}{i}\left[\delta\left(\omega-2\pi F\right)-\delta\left(\omega+2\pi F\right)\right]$$

Imaginary part is not zero