It rained heavily in the south,______serious flooding in several provinces.
A. having caused B. causing
The answer is B, but I think "having caused" shows a kind of condition. What's wrong with this option
'Having caused serious flooding in several provinces in the south, the heavy rain moved across the country to the north" is fine. It caused the serious flooding before it moved.
In your sentence, the rain started before the flooding, and it caused the flooding. Only 'causing' is appropriate.
No condition is implied in either sentence.