In the Following Proof, Which Justification Is Correct for Line

Multiple Choice

In the following proof, which justification is correct for line 7? $\begin{array}{llcc} \text { (1) \( (\exists x) \mathrm{L} x \supset(x) (\mathrm{M} x \supset \mathrm{N} x) \) } && \text {Premise } \\ \text { (2) \( \mathrm{Lb} \cdot \mathrm{Mb} \) } & \text { \(/ \mathrm{Nb}\) } & \text { Premise/Conclusion }\\ \text { (3) \( \mathrm{Lb} \) } && \text { 2 simp }\\ \text { (4) \( (\exists x) \mathrm{L} x \) } && \text { \( 3 \mathrm{EG} \) }\\ \text { (5) \( (x) (\mathrm{M} x \supset \mathrm{N} x) \) } && \text { 1, \( 4 \mathrm{MP} \) }\\ \text { (6) \( \mathrm{Mb} D \mathrm{Nb} \) } && \text { \( 5 \mathrm{UI} \) }\\ \text { (7) \( \mathrm{Mb} \) } & \end{array}$

A) 2 Add
B) 3 DM
C) 6 Simp
D) 1, 5 MP
E) None of these answers are correct.