a) if AB = CD, then 3CD = 3(CD + 1) NOT TRUE
example: AB = CD = 1, then 3CD = (3)(1)=3 and 3(CD + 1) = 3(1 + 1) = 3(2) = 6
b) if AB = CD, then AB - CD = A - C + B - D NOT TRUE (it does not make sense because A, B, C and D are points)
c) if AB = CD, then AB + EF = CD + EF TRUE
because
AB = CD |add EF to both sides
AB + EF = CD + EF
d) if AB = CD, then 2AB = 2A + 2B NOT TRUE (it does not make sense because A and B are points).
