Answer - A
The AWS documentation mentions the following:
Amazon Redshift is a fully managed, petabyte-scale data warehouse service in the cloud. You can start with just a few hundred gigabytes of data and scale to a petabyte or more. This enables you to use your data to acquire new insights for your business and customers.
For more information on AWS Redshift, please refer to the below URL:
http://docs.aws.amazon.com/redshift/latest/mgmt/welcome.html
Choices B, C and D are incorrect. Amazon Redshift is the only data warehousing service out of the choices below.