GO Classes Test Series 2024 | Mock GATE | Test 12 | Question: 33

Answer 1

To keep in mind, Ques is asking right sentential form, not viable prefix.

Just expand S and check if it can be derived or not

       A . S→ aS’ → abS’

• A. S → aS’ → a | abS’  So bS’ cant be derived
• B. S → aS’ → abS’ | a So aS’b cant be derived
• C. bbS can’t be derives

Comments

@GO Classes why can't b be the answer??

like in this S → aS’ → abS’ → abbS’

---

What you are saying is a viable prefix not a sentential  form.

sentential form is a complete state while viable prefix are the prefix of the sentential form

---

Even bS' is not a viable prefix.

The derivation that he is given is

S → aS’ → abS’ → abbS’

For 2 nd step bS' is handle so the possible viable prefixes are : a , ab , abS' and not bS'

For 3rd step bS' is handle so the possible viable prefixes are : a , ab ,abb, abbS'.