Salesforce Admin needs to import more than 2 million contacts from NetSuite to Salesforce. Which tool is the best to be used for this?

Answer options:

A.Data Export
B.Check an AppExchange app
C.Data Loader
D.Data Import Wizard

Correct Answer: C 
Option A is incorrect because Data Export is a way of taking data out of Salesforce while the salesforce admin is looking to do an import here. 
Option B is incorrect because app Exchange is a salesforce store from where you can purchase apps to extend your Salesforce capability if the out of the box features doesn’t meet your needs. 
Option D is incorrect because the Data import wizard allows you to import 50,000 records at a time. 
Reference: 

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