A fatty acid is one of the major components of a triglyceride, which is a form of lipid that is used in the body to store energy. A lipid is just a type of molecule that includes, among other things, fatty acids. Triglycerides are a secondary energy source that the body can use in the event that there is not enough sugar (our primary energy source) in the system. While fatty acids vary in terms of chemical characteristics, they all have some basic qualities in common.
Hence the right answer for the fill up the blank is "long chain fatty acids"