Despite improvements in treatment for bronchitis..

ravigupta2912 :- I would usually not negate the choices that don't make sense at all.

For eg. E discusses about urban population - a point that the author has already thrown out of consideration as evident in the premise supporting the conclusion. Even if you negate that choice it wouldn't add anything to the argument since urban population is out of consideration for the cities under discussion. Moreover, E discusses about cities with heavy urban population - not a focus of this argument

Thanks shameekv1989. So important to read carefully. I hadn't noticed the "urban" angle but now that I re read it, it makes so much sense.

Thank you.

Posted from my mobile device

(A) Urban pollution has not doubled in the past decade.
This option is not necessary for the argument's conclusion. The argument doesn't rely on whether urban pollution has doubled or not; instead, it focuses on the fact that there has been an increase in deaths from bronchitis even in cities with little or no urban pollution.

(B) Increased urban pollution, improved recording of bronchitis deaths, and the use of bronchial nebulizers are the only possible explanations of the increased death rate due to bronchitis.
This is the correct assumption. The argument dismisses the other two explanations (improved recording of deaths and increased urban pollution) and concludes that the use of bronchial nebulizers is the cause of the increased death rate. Therefore, it assumes that these three factors are the only plausible explanations, making (B) the necessary assumption.

(C) Bronchial nebulizers may cause side effects even when used according to the recommended instructions.
This statement, while possibly true, is not necessary for the argument's conclusion. The argument is concerned with whether nebulizer use is the primary cause of the increased death rate, not whether nebulizers have side effects.

(D) The use of bronchial nebulizers may aggravate other diseases that frequently occur among bronchitis sufferers.
Similar to (C), this statement, while possibly true, is not necessary for the argument's conclusion. The argument is focused on whether nebulizer use is the primary cause of the increased death rate, not whether it exacerbates other diseases.

(E) The death rate from bronchitis has shown a similar increase even in cities with heavy urban pollution.
This statement is interesting but not necessary for the argument's conclusion. The argument's focus is on the fact that the death rate from bronchitis has increased even in cities with little or no urban pollution, which suggests that urban pollution alone is not the explanation. This doesn't directly address the assumption that (B) makes, which is that there are only three possible explanations for the increased death rate.

In summary, option (B) is the correct assumption because it establishes that the three factors mentioned in the argument are the only plausible explanations for the increased death rate, thereby supporting the conclusion that nebulizer use is the cause.