In a raw text string, which of the following is used to replace spaces entered by the user?

The correct choice is plus signs (+) because in many web forms, particularly those that are URL encoded, spaces are often represented by a plus sign. When a user enters a string with spaces, such as "Hello World", it is encoded as "Hello+World" for transmission over the web. This convention is commonly used in query strings and form submissions, making the plus sign a widely recognized replacement for spaces in these contexts.

Other options, while they may have their uses in different scenarios, do not serve this specific purpose in URL encoding and form data handling. For instance, a comma, underscore, or dash might be used to format data or separate values but do not directly replace spaces in the way that a plus sign does in the context of web applications.