248.
(A) addressed; but
(B) addressing; also
(C) addressing; but
(D) addressed; also (答案A)The earliest humans did not know how to count with numbers, and it 249 them thousands of years 249 this skill. Before complicated counting systems were developed, people kept track of things through a tallying system and had to put aside one stone for each thing. Of course, this method was not perfect at all, for people would risk 250stones and would get confused when there were lots of different groups of things 250 track of.Fortunately, around 3500 B.C., the Mesopotamians invented abstract numbers for their commercial activities, and they could count much faster with these numbers. A set of symbols, called numerals, was invented to stand for the numbers.　They were little 251patterns 251 into wet clay.　Although the Mesopotamian numerals are seldom seen today, the base-60 number system used by this ancient culture still exists now.Besides the Mesopotamian number system, several other civilizations also developed their own number systems. Egyptian numerals 252 little pictures, such as 252of frogs and lotus flowers. Roman numerals like I, V, X, etc., can still be found on the face of clocks and on some official documents. Today, the most commonly used numbers are based on the Hindu-Arabic system, which is a base-10 system. By 1500, this system 253 popular in Western Europe, and then it began to spread all over the world.We all count 254 numbers every day 254 countless numbers of ways. We should be thankful that now we don’t need stones to count things anymore!