1. Eliminate all useless, unit and -productions form the following grammar: Sa.AabBCABBbCSc 2. Eliminate all useless, unit and -productions form the following grammar: S0A001BA0D1DB10ACA000B0D0 3. Construct a PDA recognizing L={0k1l2ml=k+m and k,l,m0}. 4. Construct a PDA and a CFG recognizing L={amb2ncnd2mm,n0}