og253引发的问题

253. 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

1。which问题：a and b which,which是指代a 和b,还是b呢，是不是有后面的谓语来定

2(E) (E) having been colder and wetter than was usual in some regions and slowed

是否 having been 总是错呢，什么时候用呢