There are three reading passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice and mark the corresponding letter on the Answer Sheet with a single line through the center.The sentence "most of the best things have already been located" could mean ______ . A．most of the best things have already been changedB．most of the best things remain to be changedC．there have never been so many best things waiting to be discoveredD．most secrets of the world have already been discovered