1、 A Leg Walking RightHere are some signs + - x…， the signs are very different. They mean very different things. When you see them， you know what to do. This sign + means that you will add some numerals. This sign—means that you will take one numeral away from another. You will subtract（减去）. What will you do when you see x and… ?Our signs are easy to read. They are easy signs to remember. Look at these two signs… .The ancient Egyptians used these signs. A picture of a leg walking to the left told them to add some numerals. A picture of a leg walking to the right told them to subtract. In the 1500s people used this printed（印刷的） sign  to add numerals. After a while the sign began to look like this… .Later， the sign became +.How much is 2+2?the signs are very different， They mean very different things.（   ）