The correct answer is A. Simple File Upload. Relativity's Simple File Upload documentation states that the Viewer supports the ability to replace natives and images from the Document Actions menu. The same documentation ties this replacement workflow to Simple File Upload , explaining that if you want to replace a document rather than upload a new one, you use the Replace document native function in the Review Interface. Relativity's review interface guide also shows that reviewers can replace the native file of the current document and replace the images for the current document from the Viewer.
The other tools do not match this Viewer-based replacement workflow. Mass Replace updates field values, not the native or image file itself. Relativity Processing is for ingestion and extraction workflows, not replacing a currently loaded document in the Reviewer Interface. Native Imaging Sets image groups of documents but are not the tool identified for replacing a native or image from within the Viewer. Therefore, the correct answer is Simple File Upload .