Nataliya is right.  Only 2 points are needed to define a straight line.  Maybe your teacher asked for 3 points in order to do a self-check.  An error on one of the points would not likely give you a straight line.

Although you only need two points to create a line, many mathematicians use three to five points. The reason behind that is when you start sketching parabolas, you will need to use more points to see the entire graph. You also need to use both negative and positive ordered pairs (points), as you may not be able to see the parabola's direction change unless you have both negatives and positives.

Who ever wrote that test forgot the geometric postulate: "Through any two points, there is exactly one line." 
Thus, to draw the line you need at least two points.

Points!!!!!!!

that question should be worth 3 points on a test.

You need at least 3 points to sketch the line.