Rearrange the following six sentences (A). (B), (C), (D), (E) and (F) in the proper sequence to form a meaningful paragraph; then answer the questions given below them.
(A) As a consequence, even if it is plausible that ambient air pollution plays a role for the onset and increasing frequency of respiratory allergy, it is not easy to prove this conclusively.
(B) Another factor clouding the issue is that laboratory evaluations do not reflect what happens during natural exposure when atmospheric pollution mixtures are inhaled.
(C) Interpretation of studies are confounded by the effect of cigarette smoke, exposure to indoor pollutants and to outdoors and indoors allergens.
(D) However, despite evidence of a correlation between the increasing frequency of respiratory allergy and the increasing trend in air pollution, the link and interaction is still speculative.
(E) Allergic respiratory diseases such as hay fever and bronchial asthma have indeed become more common in the last decades in all industrialized countries and the reasons for this increase are still debated.
(F) Several studies have shown the adverse effects of ambient air pollution on respiratory health.