Which formal grammar type has production rules whose left-hand side is a single non-terminal symbol?

• A. Context-Free Grammar
• B. Regular Grammar
• C. Context-Sensitive Grammar
• D. Unrestricted Grammar

Answer: (A)

In grammars, having a single non-terminal on the left side of every production defines a context-free grammar. In this form, rules look like A -> w, where A is a non-terminal and w can be any string of terminals and non-terminals. This setup lets you rewrite one non-terminal at a time and build up complex, recursive structures, which is exactly what context-free grammars are designed to express. Regular grammars are actually a narrower subset that keeps the left side as a single non-terminal but imposes a stricter shape on the right side (typically a terminal with at most one non-terminal, or just a terminal). Context-sensitive grammars relax the left-hand side, allowing longer strings of symbols, and unrestricted grammars remove such restrictions altogether. So the rule form described corresponds to context-free grammars.