The correct answer is C. Restoration.
A. Resurrection is the act of bringing someone or something back to life. This is not possible for old paintings, as they are inanimate objects.
B. Retrieval is the act of getting something back. This could be used in the context of restoring an old painting, but it is not the most common word used to describe this process.
C. Restoration is the act of repairing or preserving something to its original condition. This is the most common word used to describe the process of restoring an old painting.
D. Resumption is the act of starting something again after it has been stopped. This is not the most common word used to describe the process of restoring an old painting.