The correct answer is statement number 3. A line is an undefined term because it describes something that does not have width or depth. However, lines can extend its length in both side infinitely. It contains arrowheads indicating it can extend.
The terms point, line, and plane are referred to as undefined. When you write the definition of these terms, you have to rely on other terms that need defining. For these types of terms, mathematicians use a general description of the meanings instead of a formal definition. Answer is a term that does not have a formal definition.
