Read the following text: Plastic grocery bags are a relatively recent Invention. Polyethylene, the substance used to create plastic, was created in 1933. In 1953, a denser plastic was invented, which was used to make
plastic grocery bags. First, a company called Celloplast requested a patent for plastic tubing in 1960. Then, Gustaf Thulin Sten had the idea of removing some of the plastic to create handies. The
patent for plastic bags in the shape of a t-shirt was obtained in 1965. Finally, the Mobil Chemical company began to produce plastic bags in 1977. These plastic bags were introduced to America in
1979. However, the plastic grocery bags were not widely used or accepted. In 1985, a speaker at a regional conference explained that plastic bags were more cost-efficent than paper. By the end
of 1985, most supermarkets carried plastic grocery bags.
a: cause and effect
b: chronological order
c: compare and contrast
d: problem and solution