The correct answers are A. Build an approval process that requires unanimous approval from the manager and VP of Sales and D. Create a flow that submits the record for an approval process.
The requirement is not just to notify users or block the change. The manager and VP of Sales must review the close-date delay. Salesforce approval processes are designed to automate how records are approved, including approval steps, approvers, and approval/rejection actions.
A is correct because an approval process can route the Opportunity to the manager and VP of Sales for approval. Requiring unanimous approval ensures both reviewers must approve the delayed close date.
D is correct because a record-triggered flow can detect when the Opportunity Close Date changes and is delayed by more than 60 days, then use the Submit for Approval action. Salesforce Flow supports prior-value/change logic in record-triggered flows, and Salesforce documents the Flow Submit for Approval action.
Why others are incorrect:
B is incorrect because a validation rule blocks saving the record. It does not allow manager/VP review.
C is incorrect because a formula field and email alert do not create an approval review process, and the stated logic does not satisfy the approval requirement.

The correct answer is C. Developer sandbox.
For small, individual projects where teams need separate environments before moving work into a larger shared testing sandbox, a Developer sandbox should be considered first. It is intended for development and testing of configuration changes in an isolated environment and is the lowest-cost sandbox option compared with Developer Pro, Partial, and Full sandboxes. Salesforce describes sandbox types for different testing and development needs, with Developer and Developer Pro sandboxes copying configuration/metadata rather than full production data.
Developer Pro provides more storage, but the question emphasizes small projects and keeping costs down. Partial and Full sandboxes are better for broader testing with data, but they are not the first choice for many small isolated development efforts.

The correct answer is C.
Universal Containers wants to accept clean data and verify that important fields are entered. The best solution is a validation rule, because validation rules verify that data entered by users meets defined standards before the record can be saved. This is stronger than making a field required only on a page layout, because validation rules can enforce requirements based on conditions such as record type.
A is weaker because page-layout required fields apply mainly to that UI layout and do not provide the same conditional data-quality enforcement. B is reactive cleanup after bad data exists. D can calculate or display a value, but it does not enforce user data entry by itself.

The correct answers are A. Use a master-detail relationship between the Park and Trail objects and C. Use a roll-up summary field on the Park record to show the total number of trails.
To show the total number of child Trail records on the parent Park record without code, the app builder should use a roll-up summary field. Salesforce documentation states that roll-up summary fields display values on a master record based on related detail records.
That means Park should be the master object and Trail should be the detail object. Then a roll-up summary field on Park can count the related Trail records.
B is incorrect because standard lookup relationships do not support roll-up summary fields.
D is incorrect because a formula field cannot count multiple child records.

The correct answer is B. Apex unit test failures.
When installing a package that contains Apex in a production org, Salesforce runs Apex tests as part of the installation/deployment validation. Salesforce documentation states that package installs or upgrades can fail when Apex test requirements are not met.
Even though the unmanaged package was tested in a Full Copy sandbox, production installation can still fail if Apex tests fail during production validation.
Why others are incorrect:
A, C, and D are not the best answer because the package already installed successfully in a Full Copy sandbox that matched production. The most certification-relevant reason for production failure is Apex unit test failure.