Question

Which of the following statements is/are true?

• A. LL(1) parser uses backtracking
• B. For a grammar to be LL(1), it must be left-recursive
• C. For a grammar to be LL(1), it must be left-factored
• D. The LL(1) parsers are more powerful than the SLR parsers

Hint:

LL(1) needs the very next token alone to pick a production, so anything that makes two alternatives start the same way (a shared prefix, or infinite left recursion) breaks that requirement and must be removed first.

Answer 1

The Correct Option is C

Step 1: Recall what LL(1) parsing means.
LL(1) stands for Left-to-right scan, Leftmost derivation, using 1 token of lookahead. The entire design goal of LL(1) parsing is that the single next token always tells the parser deterministically which production to apply, so it never has to guess-and-retry. This is what distinguishes it from weaker top-down methods.

Step 2: Evaluate option (A): "LL(1) parser uses backtracking".
Because the 1-token lookahead is required to uniquely determine the next move, a correctly functioning LL(1) parser never needs to undo a choice and try another production. Backtracking parsers are a separate, less efficient class of top-down parsers used precisely when this determinism is not available. So option (A) is false.

Step 3: Evaluate option (B): "For a grammar to be LL(1), it must be left-recursive".
This has the requirement backwards. A left-recursive rule such as \(E \rightarrow E + T\) would make a top-down predictive parser recurse on \(E\) forever without consuming any input, so left recursion must always be eliminated before a grammar can be LL(1); left recursion is forbidden in an LL(1) grammar, not required. Option (B) is false.

Step 4: Evaluate option (C): "For a grammar to be LL(1), it must be left-factored".
If two productions for the same nonterminal share a common prefix (for example \(A \rightarrow \alpha\beta_1 \mid \alpha\beta_2\)), the parser cannot decide which one to expand after seeing only the first lookahead token, since both begin the same way. Left-factoring rewrites such productions to defer the choice until the strings diverge, which is a necessary transformation for the grammar to satisfy the LL(1) condition (disjoint FIRST sets per alternative). So option (C) is true.

Step 5: Evaluate option (D): "The LL(1) parsers are more powerful than the SLR parsers".
In terms of the class of grammars each method can handle, the standard hierarchy is LL(1) grammars \(\subseteq\) SLR(1) grammars \(\subseteq\) LALR(1) grammars \(\subseteq\) LR(1) grammars: every LL(1) grammar can be parsed by an SLR(1) (bottom-up) parser, but there are SLR(1) grammars that are not LL(1) (for example many grammars with common prefixes that are hard to left-factor, or that need more context). So SLR is at least as powerful as LL(1), not the other way around, and option (D) is false.

Step 6: Conclusion.
Only option (C) is a true statement.
\[ \boxed{\text{Correct option: (C)}} \]