"All of the grass clippings, dust, and pollen in the air caused my allergies to flare up wildly" (A) is the sentence which presents a cause-and-effect structure.
In a sentence with this type of organisation of ideas, you should be able to identify 2 events which are linked by causation. This means that one event (the effect) happened as a consequence of the other (the cause). Here, the speaker experienced allergic reactions as a result of the grass, dust, and pollen flying around (probably after his/her father had mown the lawn).
The cause and the effect are usually linked by a pivot verb which clearly indicates the causation. In this case, it's very obvious, because the verb is "caused."