G1 is a context-free grammar with start symbol S1, and no other nonterminals whose name begins with "S." Similarly, G2 is a contextfree grammar with start symbol S2, and no other nonterminals whose name begins with "S." S1 and S2 appear on the right side of no productions. Also, no nonterminal appears in both G1 and G2.

To combine the symbols and productions of G1 and G2 to form a new grammar G, whose language is the concatenation of the languages of G1 and G2. The start symbol of G will be S. All productions and symbols of G1 and G2 will be symbols and productions of G. Which of the following sets of productions, added to those of G, is guaranteed to

make L(G) be L(G1)L(G2)?

a) S S1S3S2, S3

b) S S1S3, S3 S1S2

c) S S1S2 |

d) S S2S1

Explain plz helps me to learn for my exam. Answer??