A saturated compound is a compound having the full complement of hydrogen atoms for every carbon atom while an unsaturated compound does not contain the full complement of hydrogen atoms for every atom of carbon.
If we look at C3H4, the only possible structure of the compound is H2C=C=CH2. We can see from this arrangement that the compound contains a cumulative double bond. This is the specific structure that fits into one of the descriptions in the options, the compound contains two double bonds.
