Problem 7. (33 POINTS) You are given three sorted sequences of lgn,n and n2 keys respectively. Let these sequences be denoted by A,B,C respectively. You are asked to generate an array D that contains all the keys that are common to all three sets A,B,C, i.e. dD if and only if dA and dB and dC. How fast can you find and generate D ? Explain by providing an efficient algorithm; analyze its worst-case running time