One reason why more young people lose their virginity during the summer than at other times of the year undoubtedly is because school vacations give adolescents more free time.

(A) One reason why more young people lose their virginity during the summer than at other times of the year undoubtedly is because

(B) If young people lose their virginity more during the summer than other seasons, it is undoubtedly because

(C) One undoubtable reason that young people lose their virginity more during the summer than other times is

(D) One reason more young people lose their virginity during the summer than at other times of the year is undoubtedly that

(E) Young people lose their virginity more often during the summer undoubtedly because, for one reason,


Whats the diff between A and D ?

Please explain.