what should your plan specify?

You are planning an upgrade to a SharePoint 2010 application. You have the following requirements:
Modify an existing workflow to include a new code activity.
.Ensure running instances of the workflow continue to work.
.Ensure new instances of the workflow include the modifications.
You need to plan the upgrade the application to meet these requirements.
After the workflow code is modified, what should your plan specify?

A.
Deploying the code to the global assembly cache (GAC) and deactivating the workflow feature.

B.
Incrementing the version of the workflow assembly, deploying to the GAC, and activating the workflow feature.

C.
Incrementing the version of the workflow assembly, deploying to the GAC, deactivating the workflow feature, and then activating the workflow feature.

D.
Incrementing the version of the workflow assembly, deploying to the GAC, and modifying the appropriate work flow. xml file to reference the new version.