In an AWS Setup of a company, a web-based application has a fleet of 10 EC2 instances. 7 EC2 instances are present in Availability Zone A, whereas 3 EC2 instances are in Availability Zone
B. The percentage (%) of requests received in Availability Zone B is greater than the percentage (%) of requests in Availability Zone A. What can be done at the architecture level to balance the load across the two availability zones? 

Answer options:

A.Use X-forwarded headers
B.Enable “split traffic equally” checkbox under load balancer configuration.
C.Use Cross-Zone load balancing.
D.Use Sticky Sessions.

Answer: C
Cross-zone load balancing
The nodes for your load balancer distribute requests from clients to registered targets. When cross-zone load balancing is enabled, each load balancer node distributes traffic across the registered targets in all enabled Availability Zones. When cross-zone load balancing is disabled, each load balancer node distributes traffic only across the registered targets in its Availability Zone.
Option A is incorrect because X-forwarded headers are not used to distribute the traffic.
Option B is incorrect because it is just a distractor, there is no such configuration.
Option D is incorrect because the sticky session feature is used to enable the load balancer to bind a user`s session to a specific target. This ensures that all requests from the user during the session are sent to the same target. 
Reference:
https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/how-elastic-load-balancing-works.html#availability-zones
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/sticky-sessions.html
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/x-forwarded-headers.html