a) Explain the following concepts: i) Entity integrity ii) Referential integrity iii) Foreign key b) Explain advantages of indexing over sorting commands c) List any four aggregate SQL functions d) Write FoxPro program stub that assigns a value 40 to all elements of a 2 x 3 array e) Interpret the output of the following FoxPro statements: ? Strl + Str2 and ? str1 - str 2 Where Strl = 'Hellow' Str2 = 'World'