NTA | UGC NET 2019 December | Question 1

Consider the language L = {anbn-3 | n>2} on Σ = {a, b}. Which one of the following grammars generates the language L?

(A)

 S → aaaA | λ, A → aAb | λ

(B)

S → aaA | λ, A → aAb | λ

(C)

S → aaaA | a, A → aAb | λ     

(D)

S → aA | a, A → aAb | b

Answer: (D)
Explanation:

For n=3, String generated= aaa

For n= 4, String generated = aaaab

For n =5, String generated = aaaaabb

Only, option 4 can generate the above grammar at following values of n. 

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