Answer: (2),(3) and (5) Step-by-step explanation: It is given that BEC is a triangle, then ∠BEC is an interior angle of the triangle BEC and not the exterior angle, thus option (1) is incorrect. In the given triangle, ∠DEC is an exterior angle as it is outside the given triangle BEC, thus option (2) is correct. Two-column proofs serve as a way to organize a series of statements (the left hand column), each one logically following from prior statements. The justifications (the right-hand column) can be definitions, postulates (axioms), properties of algebra, equality, or congruence, or previously proven theorems. The problem is , this list is very big and I am not sure that it can be considered as a key , because its size is larger than the secret message. * Secret Image size is (128*128) = 16 KB * key ...