Requirements analysis and feasibility study is correct. This is the phase where stakeholders capture functional and nonfunctional requirements and where acceptance criteria and testable requirements should be identified and recorded so tests can be planned and traced back to requirements.

During the Requirements analysis and feasibility study teams define what the system must do and how success will be measured. Clear acceptance criteria and test conditions are created at this time so design and implementation can be verified against them and so test planning, test design, and traceability can proceed early and effectively.

Implementation and coding is not correct because coding is the activity where developers build the solution and implement unit and integration tests, but it is too late to discover core acceptance criteria. Acceptance criteria should already be available when coding begins.

Maintenance phase is not correct because maintenance occurs after release and fixes or enhancements are applied. Defining initial testing requirements and acceptance criteria in maintenance would leave the original development without clear verification targets.

Test execution phase is not correct because execution is when tests are run against a build. If acceptance criteria and testing requirements are not defined before execution then tests cannot be properly designed or traced back to requirements, and execution becomes ad hoc rather than systematic.

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