$\definecolor{red}{RGB}{255,0,0}$$\definecolor{black}{RGB}{0,0,0}$
  1. D
  2. D
  4. D
    • D  =   a·d-b·c
  1. a
  2. a
  4. a
  1. b
  2. b
  4. b
  1. c
  2. c
  4. c
  1. d
  2. d
  4. d