You are using lifecycle hooks in your AutoScaling Group. Because there is a lifecycle hook, the instance is put in the Pending:Wait state, which means that it is not available to handle traffic yet. When the instance enters the wait state, other scaling actions are suspended. After some time, the instance state is changed to Pending:Proceed, and finally InService where the instances that are part of the Autoscaling Group can start serving up traffic. But you notice that the bootstrapping process on the instances finishes much earlier, long before the state is changed to Pending:Proceed. 

Answer options:

A.Use the complete-lifecycle-action call to complete the lifecycle action. Run this command from another EC2 Instance.
B.Use the complete-lifecycle-action call to complete the lifecycle action. Run this command from theCommand-line interface.
C.Use the complete-lifecycle-action call to complete the lifecycle action. Run this command from the Simple Notification service.
D.Use the complete-lifecycle-action call to complete the lifecycle action. Run this command from an SQS queue.

Answer – B
The AWS Documentation mentions the following.
3. If you finish the custom action before the timeout period ends, use the complete-lifecycle-action command so that the Auto Scaling group can continue launching or terminating the instance. You can specify the lifecycle action token, as shown in the following command:
For more information on lifecycle hooks, please refer to the below URL:
http://docs.aws.amazon.com/autoscaling/latest/userguide/lifecycle-hooks.html