Confirm selection of a single file?

In our application, user has the ability to import projects from a CSV file. It is done using modal dialog in which there is a description of the import, link to an example file and a clickable dropzone in which the user can either drop the csv file or select a file by clicking.

The only action that can be done in this dialog is selecting the file. The user cannot cancel or revert the import during upload nor after it completes.

A) Should the import start right after the user selects the file or

B) should the user confirm the file selection by clicking a confirm button?