When the electric field strength is large, electric field lines are: a) close together.
b) perpendicular to each other.
c) electric field lines are not related to the field strength.
d) far apart.
e) none of the above.

a) close together

Explanation: The electric field lines also  represent the intensity of the field, in this sense  for strong electric fields it is usually draw the lines close to each other. In constrast when they are far apart the electric field is weak.  

this is poiselle's equation from fluid mechanic in physics. mech eng