Which of the following is a valid deletion rule? A. Q-deletion B. R-deletion C. S-deletion D. T-deletion

In the context of theoretical computer science and formal languages, particularly concerning the study of grammar and language parsing, deletion rules refer to specific transformations applied to strings or structures. They typically involve the removal of specific symbols or elements under certain conditions.

Among the options provided—Q-deletion, R-deletion, S-deletion, and T-deletion—the most commonly discussed deletion rules are those associated with the transformation of grammar and languages. While it's important to note that the validity of each rule may depend on the specific framework or theory being applied, generally:

• S-deletion is the most recognized in literature, particularly related to context-free grammars and various forms of formal languages.

Thus, among the given options, "C. S-deletion" is the most likely to be a valid deletion rule in accepted theoretical contexts. If you're looking for specific definitions or applications, further context about the rules' application could provide a clearer answer.