Concept:Subsidiary books are books of original entry where similar transactions are first recorded before posting to the ledger.
Explanation:The cash book records all cash and bank transactions.
It is a subsidiary book because it serves as the book of original entry for these transactions.
A bank statement is an external record issued by the bank, not a book of account.
Control accounts are ledger accounts that summarize other accounts.
A trial balance is a statement of ledger balances, not a subsidiary book.
Therefore, the only subsidiary book among the options is the cash book.
Answer:A. cash book