A Molecule in a Uniform Ideal Gas Can Collide with Other

A molecule in a uniform ideal gas can collide with other molecules when their centres are equal to or less than:

A) one radius away from its centre.
B) one diameter away from its centre.
C) two diameters away from its centre.
D) twice the cube root of volume away from its centre.
E) $\sqrt{2}$ diameters away from its centre.