You have a Feature named Feature1.

You plan to create a new version of Feature1 that will upgrade the existing version of Feature1.

You need to ensure that when Feature1 is upgraded, additional configuration data is added to the property bag of the site.

What should you do?

A.
Add a <CustomUpgradeAction> element and increase the Version number of the Feature.

B.
Add a <CustomUpgradeAction> element and increase the UIVersion number of the Feature.

C.
Add an <ActivationDependencies> element and increase the Version number of the Feature.

D.
Add an <ActivationDependencies> element and increase the UIVersion number of the Feature.

Explanation:
MNEMONIC RULE: “CustomUpgradeAction Version”

<CustomUpgradeAction> Allows you to execute custom code when a Feature instance is being upgraded.

Feature.xml Changes
http://msdn.microsoft.com/en-us/library/ee537575.aspx