Answer
B) By how close the lines are.
Step-by-step explanation
Electric fields lines are used to convey information about the electric field. Electric field lines are drawn such that they point in the direction a positive test charge would go when placed in any particular point space. In this sense, electric field lines give information about the direction of the electric field in the space around a charge.
The other piece of information that electric field lines convey is strength of the field in the space around the charge. The closer the lines are to each other, the stronger the field the closer the lines are to each other. An illustration of this point is that near the charge where the lines originate, it is known that the electric field is stronger. When drawn electric field lines are closer to each other near charges than they are far away from charges.