根据以下内容回答题： Which is the most important invention?If you（1）toothbrush，then you agreed with42％of the people who were asked the（2）question in a sunrvey done by Massachusetts In-stitute of Technology． Apparently，people have wanted clean teeth for a long time．From as far back as 3，000 B．C．there is（3）of people chewing pieces of wood to clean their mouths．In Roman times，people began to clean their teeth by rubbing them with（4）of cloth．But neither of these（5）was particularly effective． So who deserves the credit for the low-tech，（6）efficient invention of the toothbrush?A Chinese emperor made the first toothbrush in 1498．It（7）hard animal hair stuck into a piece of bone．But toothbrushes didn’t become（8）immediately．They weren’t（9）known until the l600s．Even then，they were so expensive that all the family members in a house usually（10）one!Toothbrushes have come a long way since then．Nowadays，there are many versions for sale from basic，practical ones to state-of-the．art electric ones． 1.