How can an element be identified using its emission spectrum? a. by measuring the frequencies of the spectral lines, and calculating the energies that these correspond to b. by measuring the wavelengths of the spectral lines, and then calculating the differences between adjacent wavelengths c. by heating the unknown element, and then comparing the emitted spectrum with known spectra of the elements d. by identifying the color of the first line of the spectrum, and comparing this to a chart of known spectra