Your company has a set of EC2 Instances that access data objects stored in an S3 bucket. Your IT Security department is concerned about the security of this architecture and wants you to implement the following

Answer options:

A.Create an IAM user and ensure the EC2 Instances uses the IAM user credentials to access the data in the bucket.
B.Create an IAM Role and ensure the EC2 Instances uses the IAM Role to access the data in the bucket.
C.Use S3 Cross Region replication to replicate the objects so that the integrity of data is maintained.
D.Enable versioning on the objects and ensure that MFA Delete is set on the objects in the bucket

Answer - B and D
The AWS Documentation mentions the following
IAM roles are designed so that your applications can securely make API requests from your instances, without requiring you to manage the security credentials that the applications use. Instead of creating and distributing your AWS credentials, you can delegate permission to make API requests using IAM roles 
For more information on IAM Roles, please refer to the below link:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html
MFA Delete can be used to add another layer of security to S3 Objects to prevent accidental deletion of objects ( it is upto the user to check for accidental deletion of the objects even after implementation of MFA )
For more information on MFA Delete, please refer to the below link:
https://aws.amazon.com/blogs/security/securing-access-to-aws-using-mfa-part-3/