The Following Events Pertain to Bills Company: Using Cash-Basis Accounting,on

The following events pertain to Bills Company: Using cash-basis accounting,on which date should Bills Company record revenue for the accounting and tax services?
$\begin{array}{|l|l|}\hline\text { December } 28,2018 & \begin{array}{l}\text { Bills was contacted by a customer for possible accounting and tax } \\\text { services. }\end{array} \\\hline \text { December } 30,2018 & \begin{array}{l}\text { Bills signed a formal agreement with the customer to provide } \\\text { accounting and tax services in } 2019 .\end{array} \\\hline \text { January } 4,2019 & \begin{array}{l}\text { The customer paid } \$ 1,000 \text { in advance for the services to be provided } \\\text { by Bills Company. }\end{array} \\\hline \text { January } 11,2019 & \text { Bills provided accounting and tax services to the customer. } \\\hline\end{array}$

A) December 30,2018.
B) December 31,2018.
C) January 4,2019.