Step 1: Analyze Statement I
"All books are ledgers."
This statement implies that every book is a ledger, so the set of books is entirely contained within the set of ledgers.
Step 2: Analyze Statement II
"All pens are keys."
This statement implies that every pen is a key, so the set of pens is entirely contained within the set of keys.
Step 3: Analyze Statement III
"Some pens are books."
This statement implies that there is some overlap between the sets of pens and books. Therefore, some pens are also books.
Step 4: Evaluate Conclusion I
"Some ledgers are keys."
Since all books are ledgers, and some pens (which are also keys) are books, it follows that there is at least some overlap between ledgers and keys. Therefore, conclusion I is true.
Step 5: Evaluate Conclusion II
"Some keys are books."
Since some pens are both books and keys, it follows that some keys are books. Therefore, conclusion II is also true.
Step 6: Final Answer
Both conclusions I and II follow from the given statements.
Final Answer: The correct answer is (d) both I and II follow.