Suppose you look at a spectrum of visible light by looking through a prism or diffraction grating. how can you decide whether it is an emission line spectrum or an absorption line spectrum?

an emission line spectrum consists of bright lines on a dark background, while an absorption line spectrum consists of dark lines on a rainbow background.
an emission line spectrum consists of a long bright line, while an absorption line spectrum consists of a long dark line.
the only way to decide is to make a graph of the intensity of the light at every wavelength, and then analyze the graph carefully.
the emission line spectrum is produced by electrons jumping up in energy level, while the absorption line spectrum is produced by electrons jumping down in energy level.