Lines 47-56 determine the central idea of these lines

the unsaturated fatty acid is a fat consist of one or more double bond in the fatty acid chain. if it contains one double bond then called as monounsaturated fatty acid however if, it contains more than one bonds called as a polyunsaturated fatty acid. true fatty acids are called unsaturated fatty acids as it reduces the risk of high blood cholesterol and good for health.

alone =having no one else present.