Benjamin Franklin was born on January 17,1706 in Boston,America. In his life he built a successful printing and publishing business in Philadelphia;he conducted scientific studies of electricity and made several important discoveries;he was a diplomat   and statesman;he helped establish Pennsylvania's first university and America's first city hospital;he also organized the country's first subscription library  . Franklin was also _ in America as an inventor until Thomas Edison. Ben had poor eyesight  and needed glasses to read. He got tired of always taking them off and putting them back on,so he decided to figure out a way to make his glasses let him see both near and far. He had two pairs of glasses cut in half and put half of them together. Today,we call them bifocals  .Another invention of his,an iron stove,allowed people to warm their homes. He loved to learn about new things. He also thought it was important to make life better with the things that he invented. Electricity was one of the things he experimented with when he retired from his business. Ben discovered that lightning   and electricity were the same thing. The lightning rod was an important invention that we still use today to protect buildings and ships from lightning damage. Franklin preferred to have his inventions used freely for the comfort and convenience of everyone. Thomas Jefferson,the third president of America,called Benjamin Franklin "the greatest man of the age and country in which he lived".To Benjamin Franklin there was no greater purpose in life than to "live usefully". Which of the following is NOT Benjamin's invention?
Bifocals. The iron stove. Printing. The lightning rod.