This is because the proportion is saying that side BC over side YZ is the same as 28 over 14. This is correct because 28 and 14 are the actual lengths of these sides of the triangle. The other choices do not relate to the same sides of both triangles.
You could draw a line that bisects one line at 90% and if it bisects the other line at 90% too they are parallel but you need a protractor or a compass