Question: How is P related to Q? Statement I: P is the only son of Q's mother. Statement II: Q is the sister of R. Which statement(s) are sufficient to answer the question?

Statement I: P is the only son of Q's mother, so P and Q share the same mother and P is male — P is Q's brother. Sufficient. Statement II relates Q to R only, saying nothing about P — insufficient. Statement I alone is sufficient.