To solve this problem, we need to identify which of the given options is a natural polymer.$\newline$Let's analyze each option:$\newline$• Option 1: poly (Butadiene-styrene) is a synthetic polymer, commonly known as SBR (Styrene-Butadiene Rubber).$\newline$• Option 2: polybutadiene is also a synthetic polymer, used in the production of tires and other rubber products.$\newline$• Option 3: poly (Butadiene-acrylonitrile) is a synthetic polymer, known as NBR (Nitrile Butadiene Rubber), used for making oil-resistant products.$\newline$• Option 4: cis-1,4-polyisoprene is a natural polymer, commonly known as natural rubber. It is obtained from the latex of rubber trees.$\newline$Therefore, the correct option is Option 4, as cis-1,4-polyisoprene is a natural polymer.