Comprehensive and Detailed Explanation From Exact Extract:

From theCTFL-AT Syllabus v4.0, Section 4.2Continuous Integration, it states:

"Continuous integration involves integrating code into a shared repository several times a day. Each integration is verified by an automated build and automated tests."

Hence,Option D—at least once a day— correctly reflects best practice in continuous integration.

Option A(once per iteration) andB,Care far too infrequent to meet the goals of CI.

The objective is to detect integration issuesearly and often, which is only achievable throughdaily (or more frequent)integrations.