Which of these best describes an undefined term? a. a term that is a building block for other definitions in geometry b. a clause in a conditional statement that begins with "then" c. a statement that has already been proven to be true d. a statement that is the opposite of an original statement

Step-by-step explanation:

In Geometry, undefined terms refer to concepts like point, line and plane. Which are concepts that cannot be defined, they are too intuitive. Undefined terms are always true, they cannot be prove because those concepts are too primitive.

It's important to know that Geometry develops another complex defintions from these undefined terms, beacuse point, line and plane are the fundamentals of Geometry.

Therefore, the right answer is A.

Other choices are just wrong, because undefined terms aren't condition statments, they cannot be proven and they aren't oppsite of an original statement.