Analysts blamed May's sluggish retail sales on unexciting merchandise

The concept of the present participle (verb+ing) modifying with or without the comma preceding it has the following significance IMO. Of course, as Zorralou has rightly said, without the comma, there is not much confusion, as it forthrightly modifies the preceding noun.
But in the case of the comma preceding, we all know it modifies the entire preceding clause. What exactly is meant by the preceding clause? Some have said it is the subject, some others say it is the verb because it is an adverbial modifier. May be they are correct in their own right. But more importantly, and very often, it highlights the gist of the entire preceding clause and not just a part of it.
Let’s see how in this given case; Now, slowing is the participle under question. Something has caused the slowing. Is it the weather alone or the unexciting merchandise alone or both put together? You will appreciate it is both together that have contributed to the slowing. Logically analysts cannot contend for being modified as, their job is just to pass appropriate comments. So the modified parts are really the merchandise and the weather put together, both noun forms objects of the verb blamed; so, the whole gist is about the result of some things impeding something collectively in the context.

In the light of the above, we have to dump all the choices that pinpoint something with a relative pronoun, (which) Choices A and C fall under this category. Choice E uses the verb –slowed- as an action of the noun weather, which is a fractured meaning from the original intent.
Between B and D, both use the verb+ ing preceded by a comma. But the use of ‘being’ colder and wetter in D is unnecessarily superfluous; being used as a modifier of weather, is not acceptable; B even without the word being is crisp and tidy.
So B overrides D.