Jane Petrosyan represents a typical customer who makes an online purchase via a locally run company called CloudShoppers Boutique Inc. $($CSB$)$ in Albany, New York.

Including Jane, CSB has $10,000$ customers in Albany. The company hosts $100$ servers including Web, Database, Authentication, and Business Application servers for its customers in the Albany data center.

Jane's request from her laptop prompts the use of one Authentication, one Web, one Database, and one Business Application Server at CSB$\text{'}$s Albany data center.

Question: CSB$\text{'}$s client$/$server or application is an n$-$tier architecture, where n is equal to:

Group of answer choices

$101($since there are $101$ devices including Jane's laptop$).$

$5($since there are four servers and one customer's computer or smartphone used to address a typical customer's transaction request$).$

$4($since there are four servers used to address a typical customer's transaction request$).$

$10,100($since there are $10,000$ customers, and $100$ servers at CSB$).$