Answer:
c. January 4, 2019.
Explanation:
Accrual Basis of Accounting states that transactions are recorded when they meet the definition and recognition criteria of either an Asset, Liability, Income or Expense.
According to International Financial Reporting Standard (IFRS), Revenue is recorded when the entity transfers control of the goods or services (IFRS 15).
Bills Company provided accounting and tax services to the customer on 4 January. This is the date that control is transferred.
Thus, Bills Company record revenue for the accounting and tax services on January 4, 2019.