A company wants to integrate their phone system into Salesforce to automatically record call history. What would Salesforce Admin do to achieve this?

Answer options:

A.Create custom CTI application
B.Activate CTI connector
C.Contact Salesforce to enable CTI
D.Check the AppExchange for CTI partners

Correct Answer: D 
Typically, CTI vendors or partners create Open CTI implementations. After you have done an Open CTI implementation, it’s integrated with Salesforce using the Salesforce Call Center. Keep in mind that the out-of-the-box Service app is a Salesforce Classic app and only supports Open CTI for Salesforce Classic. To make calls in Lightning Experience, use Open CTI for Lightning Experience in a Lightning Experience app, like our out-of-the-box Service Console app. 
Option A is incorrect because creating custom CTI application will need a developer and lots of work to be done for this to be achieved. Also, this is beyond the capabilities of a Salesforce Administrator. 
Option B is incorrect because there is no option to activate the CTI connector without a CTI partner. 
Option C is incorrect because Salesforce cannot enable CTI if you don’t have CTI partner to have an implementation in place. 
Reference: 

https://help.salesforce.com/articleView?id=cloud_cti_api_overview.htm&type=5