UGC NET CSE | June 2019 | Part 2 | Question: 78

Question

Consider the following grammar:

$S \rightarrow XY$

$X \rightarrow YaY \mid a \text{ and } Y \rightarrow bbX$

Which of the following statements is/are true about the above grammar?​​​​​​

1. Strings produced by the grammar can have consecutive three $a$’s.
2. Every string produced by the grammar have alternate $a$ and $b$.
3. Every string produced by the grammar have at least two $a$’s.
4. Every string produced by the grammar have $b$’s in multiple of $2$.

• A. i only
• B. ii and iii only
• C. iv only
• D. iii and iv only

Answer 1

Answer. 4:(c) and (d) only

It generates strings which contains b multiple of 2 and no of a at least 2.

Answer 2

Grammar generate a string abba.

  This is satisfied by option  c and d.  But option a and b are not satisfied.  

So option c and d is right. 

Answer 3

option D) is correct , as

1. Every string produced by the grammar have at least two aa’s, it is true
2. Every string produced by the grammar have bb’s in multiple of 2 , it is also true