For which objects auto-response rules can be created? (Choose 2 options)

Answer options:

A.Cases
B.Accounts
C.Opportunities
D.Leads

Correct Answer: A and D 
Auto-response rules can be created for the leads captured through a Web-to-Lead form and for cases submitted through a: Self-Service portal
Customer Portal
Web-to-Case form
Email-to-Case message
On-Demand Email-to-Case message
An Auto Response rule is a set of conditions for sending automatic email responses to lead or case submissions based on the attributes of the submitted record. You can create as many response rules as you like based on any attribute of the incoming lead or case, but only one rule for leads and one for cases can be active at a time. 
Option A and C are incorrect because you cannot assign them auto-response rules. 
Reference:

https://help.salesforce.com/articleView?id=creating_auto-response_rules.htm&type=5