47.BD
1998 saw several new ventures promoting online distance learning both at the college and graduate level, but also faculty members in large numbers began questioning whether the computer screen was an adequate replacement for the classroom.
(A) 1998 saw several new ventures promoting online distance learning both at the college and graduate level, but also faculty members in large numbers began (B) In 1998 several new ventures were promoting online distance learning for both college-and for graduate-level courses, but it was also a year for a large number of faculty members who began (C) With several new ventures promoting online distance learning both for college and graduate courses in 1998, it was also a year when a large number of faculty members had begun (D) Although 1998 saw several new ventures promoting online distance learning for both college- and graduate-level courses, it was also a year when a large number of faculty members began (E) Several new ventures were promoting online distance learning in 1998, at both the college level as well as the graduate, but it was also a year for faculty members to begin in large numbers 不懂B中for与D中when的区别有多大。。。另外，觉得D中1998前不需要介词吗？？谢谢！！ | 
