What word requires a spelling change before adding the suffix-er? fast? merry? smart? buy?

Which statement best expresses a claim a.although many people believe homework is a crucial part of school, there is evidence to suggest that homework may not be as valuable as once thoughtb.the amount of homework given by some high school teachers is insane and actually has negative effects on other important aspects of a student's life c.i would have so much more time to do the extracurricular activities and hobbies i enjoy if i did not have to spend most of my evenings doing homework d.some schools have adopted homework policies that limit the amount of homework that teachers are allowed to assign their students each night