A - might work but it is not mentioned that old environment will be deleted, so additonal cost(double) involved here
B - rds should be separated from ebs
C - rds should be separated from ebs
D - correct. this will terminate the old environment as mentioned below
https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/environmentmgmt-updates-immutable.html
When the first instance passes health checks, Elastic Beanstalk launches additional instances with the new configuration,
matching the number of instances running in the original Auto Scaling group. When all of the new instances pass health checks,
Elastic Beanstalk transfers them to the original Auto Scaling group, and terminates the temporary Auto Scaling group and old instances.