Đáp án B
1978 . 1979 . 1980 . 21 + 1958 1980 . 1979 - 1978 . 1979 = 1978 . 1979 + 1979 + 1 . 21 + 1958 1979 1980 - 1979 = 1978 . 1979 + 1979 . 21 + 21 + 1958 1979 . 2 = 1978 . 1979 + 1979 . 21 + 1979 1979 . 2 = 1979 . 1978 + 21 + 1 1979 . 2 = 2000 2 = 1000