有一个一直搞不太明白的比较问题

依凡达

.Analysts blamed May’s sluggish retail sales on unexciting merchandise as well as the weather, colder and wetter than was usual in some regions, which slowed sales of barbecue grills and lawn furniture.
(A) colder and wetter than was usual in some regions, which slowed
(B) which was colder and wetter than usual in some regions, slowing
(C) since it was colder and wetter than usually in some regions, which slowed
(D) being colder and wetter than usually in some regions, slowing（B）
(E) having been colder and wetter than was usual in some regions and slowed



像这个题，很多人错是因为slowing，可是我觉得Bwhich was ...than usual有问题，usual前面是不需要补一个was吗
点很奇怪求大神拯救

依凡达

谢谢回复！！嘻嘻第一次发帖就有好心人，么么哒