You need to ensure that no updates are allowed to an individual site collection

You are the administrator for your company’s SharePoint environment. You are configuring a site
collection to prepare for an upgrade to SharePoint Server 2013.
You need to ensure that no updates are allowed to an individual site collection.
What should you do?

A.
In Central Administration, set the state of the site lock status to Adding Content prevented.

B.
In Central Administration, set the state of the site lock status to Read-only.

C.
In Central Administration, set the state of the site lock status to No access.

D.
In SQL Server, set the content database to read-only.

Explanation:

Option Adding Content prevented prevents users from adding new content to the site collection.
Updates and deletions are still allowed.
Manage the lock status for site collections in SharePoint 2013
https://technet.microsoft.com/en-us/library/cc263238.aspx