关于这个题目，求nn

mike125615212

A recently published report indicatesthat the salaries of teachers continue to lag far behind other

college-educatedprofessionals, because they make an average of nearly $8,000 a year less at the

start of their careers and almost $24,000less a year by the time they reach the age of 50.    

(A) other college-educated professionals,because they make an average of nearly $8,000 a year

less at the start of their careers andalmost $24,000 less

(B) other college-educated professionals,by an average of nearly $8,000 a year at the start of their

careers, to almost $24,000

(C) what other college-educatedprofessionals are paid--making an average of nearly $8,000 a year

less at the start of their careers andalmost $24,000 less

(D) those of other college-educatedprofessionals--by an average of nearly $8,000 a year at the

start of their careers to almost $24,000less

(E) those of other college-educatedprofessionals--by an average of nearly $8,000 a year at the

start of their careers, and by almost$24,000

这个题正确答案是e但是，E为什么在, and by前加了个逗号呢？求解答啊求解答！！！

mike125615212