"on having" is not gramatically correct. It is better on how to draw

Option A ; it is not proper to say 'having' a spherical earth because it is not their possession.Thers is a spherical earth but they are not in anyway having it.

Option B; Here,the same applies for 'having' ....The earth in question is not owned by them in anyway.

Option C; This option is no where near the correct answer because the statement makes it unqualified for it to be the right answer. ' how can one draw the spherical Earth on a flat sheet of paper' The sentence is non-sequitur.

Option D; how they could use a flat sheet of paper to draw the spherical Earth' this is an inverted statement which is also incorrect but depicts what the problem of the cartographers are.

Option E; This is the correct answer because the sentence is stated and clearly depicts the struggles of the Cartographers .It addresses the problem o f'how to draw the spherical earth on a flat sheet of paper'