Option A is correct because configuring REST services in B2C Commerce is a necessary step to enable authentication and communication with Marketing Cloud via its API integration and to initiate transactional email delivery using Marketing Cloud's Transactional Messaging REST API.

Option C is correct because creating an API integration in Marketing Cloud using Installed Packages is a necessary step to provision access to Marketing Cloud APIs by external systems like B2C Commerce and to generate an API key and secret for authentication purposes.

Option D is correct because customizing the B2C Commerce storefront to trigger Marketing Cloud Transactional Messages at strategic points in the customer's experience is a necessary step to invoke Marketing Cloud's Transactional Messaging REST API with a payload that informs message contents and recipients.

Option B is incorrect because front-end development capabilities are not required to configure the Marketing Cloud Connector for triggered emails, but rather to customize the B2C Commerce storefront and the email templates in Marketing Cloud.

Option E is incorrect because integrating Marketing Cloud and B2C Commerce to provide Marketing Cloud with B2C Commerce order and customer information on a nightly basis via SFTP is not required to configure the Marketing Cloud Connector for triggered emails, but rather to enable data synchronization and segmentation for marketing campaigns.

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