The graph of every linear equation in two variables will beA straight lineA curved line A parabolic curveWe can't plot its graph

The graph of every linear equation in two variables will be a straight line.

Here's why:

1. A linear equation in two variables is of the form y = mx + c, where m and c are constants.

2. The term 'linear' itself indicates a straight line.

3. When you plot this equation on a graph, you'll notice that every value of x corresponds to a single value of y. This forms a straight line.

4. Unlike quadratic equations (which form parabolic curves) or other higher degree equations (which can form various types of curves), linear equations are simple and always form a straight line.

5. Therefore, no matter what the values of m and c are, the graph will always be a straight line.

So, the correct answer is "A straight line".