See the solution in the explanation below:
Explanation
To provide only Adele Vance with the ability to turn on and off Teams preview features, you need to create and assign a custom update policy for her. Here are the steps to do so:
Sign in to the Microsoft Teams admin center with your Microsoft 365 username and password1.
In the left navigation, go to Teams > Teams Update policies.
Select Add to create a new policy or select an existing policy to open Update policy.
Name the update policy, add a description, and select Enabled from the drop-down menu for Allow public preview. This option enables Teams Public Preview regardless of whether a user is enrolled in Office Current Channel (Preview). The end user must also opt in to Teams public preview in their Teams app2.
Click Save and then Close.
In the left navigation, go to Users and then search for Adele Vance from the list of users.
In the user details page, go to Policies and then click Edit next to Assigned policies.
In the Assigned policies pane, under Update policy, select the policy that you created or modified in step
4 from the drop-down menu.
Click Apply and then Close.
Now, Adele Vance can turn on and off Teams preview features by following these steps in her Teams app3:
Select the three dots to the left of your profile to display the Teams menu.
Select About > Public preview.
Select Switch to Public preview or Switch back to standard version.

Explanation

Explanation
According to the Microsoft documentation1, to create an expiration policy for Microsoft 365 groups, you need to have one of the following roles:
Global administrator
Groups administrator
User administrator
The Groups Administrator role allows you to manage all aspects of Microsoft 365 groups, including their settings, classifications, expiration policy, and naming policy2. However, this role does not allow you to create an expiration policy for Microsoft 365 groups.
Therefore, based on this information, the correct answer is B. Request the Global Administrator role. This role has the highest level of permissions and can perform any administrative task in Microsoft 3653. Alternatively, you can request the User Administrator role, which can also create an expiration policy for Microsoft 365 groups1.

Reference:
https://docs.microsoft.com/en-us/microsoftteams/teams-and-skypeforbusiness-coexistence-and-interoperability