令X={1,2,3,4,5},R={〈1,2〉,〈3,4〉,〈2,2〉},则R◦R为()
A. {〈1,2〉,〈2,2〉,〈3,2〉}
B. {〈1,2〉,〈2,3〉}
C. {〈1,2〉,〈2,2〉,〈4,2〉}
D. {〈1,2〉,〈2,2〉}
设A={0, 1, 2},R是A上的关系:R={〈0,2〉,〈1,0〉,〈1,1〉,〈2,0〉,〈2,1〉}求R的逆关系为()
A. {〈2,0〉,〈1,0〉,〈1,1〉,〈0,2〉,〈1,2〉}
B. {〈2,0〉,〈0,1〉,〈1,1〉,〈0,2〉,〈2,1〉}
C. {〈2,0〉,〈0,1〉,〈1,1〉,〈0,2〉,〈1,2〉}
D. {〈2,0〉,〈1,0〉,〈1,1〉,〈0,2〉,〈2,1〉}