Question 1: A unit pair (X,Y) for a context-free grammar is a pair where: 1. X and Y are variables (nonterminals) of the grammar. 2. There is a derivation X =>* Y that uses only unit productions (productions with a body that consists of exactly one occurrence of some variable, and nothing else). For the following grammar: S A | B 1 2 A COLD c1 | E C D 1 E 13 EO IS E D1 S Identify all the unit pairs. Then, select from the list below the pair that is NOT a unit pair. (A,E) (C,B) (D,C) (DE)