Does a line lie in only one plane?

Answer 1

No. A line can lie in many planes. A plane can be defined by three non-linear points. Since a line is defined by only two points, we need another point. (Note that point C alone, or line AB alone belong to an infinite number of planes.)

Answer 2

Yes, a line lies in only one plane. This is a fundamental property of geometry where a line can be uniquely defined by two points and can only exist within a single plane.