In the following sentence with a blank, choose the most appropriate word to complete it: "He _____ to the problem of air pollution in his speech."

Introduction / Context:
This question tests fine distinctions between similar looking verbs in English. The sentence describes what a speaker did in relation to the problem of air pollution during a speech. The verb used must fit both grammatically and stylistically, and, in this particular case, the exam tests a relatively formal verb that many learners may not know well.

Given Data / Assumptions:

• Sentence: He _____ to the problem of air pollution in his speech.
• Options: averted, adverted, exclaimed, mentioned and alluded.
• The speaker is talking about a serious issue, so the verb should mean referred to or drew attention to.
• We assume formal written English as in competitive examinations.

Concept / Approach:
The less common verb advert, when followed by to, means to call attention to or refer briefly to something. Thus, adverted to the problem of air pollution is a precise and formal way of saying referred to the problem. Avert, on the other hand, means to turn away or prevent something, as in avert a crisis. Exclaimed means cried out suddenly, usually with emotion, and does not take to in this sense. Mentioned is possible but does not match the specific testing of the form adverted to, which is a known exam favourite. Alluded also means referred indirectly, but the standard collocation in this classical sentence is adverted to.

Step-by-Step Solution:
Step 1: Understand that the sentence requires a verb meaning referred to or drew attention to.
Step 2: Note that avert does not fit because one cannot avert to a problem; avert takes a direct object and means prevent or turn away.
Step 3: Recognise that advert, in formal usage, followed by to, means to refer to briefly.
Step 4: Compare adverted to with mentioned and alluded, and recall that many exam questions specifically test adverted to as a collocation.
Step 5: Select adverted as the most appropriate word for the blank.

Verification / Alternative check:
Read the complete sentence using the chosen verb: He adverted to the problem of air pollution in his speech. This sounds formal but correct in written English. If we use averted, the sentence becomes He averted to the problem, which is wrong because avert does not take the preposition to in this way. Exclaimed to the problem is also incorrect. Mentioned and alluded could work in casual writing, but the specific collocation adverted to is a known expression, especially in legal and formal documents. This supports adverted as the key the question is testing.

Why Other Options Are Wrong:
Option A, averted, means prevented or turned aside, as in averted a disaster, and cannot be followed by to in this context. Option C, exclaimed, means cried out in surprise or emotion, and one exclaims about something, not to a problem in a neutral statement. Option D, mentioned, although semantically close, does not showcase the particular formal vocabulary item that the question aims to test. Option E, alluded, also means referred indirectly, but the phrase alluded to the problem tends to imply a subtle hint rather than direct reference. The sentence here fits better with adverted to, which clearly signals deliberate reference in formal style.

Common Pitfalls:
Many learners simply choose mentioned because it is more familiar, but competitive exams often include less common but correct words to reward precise vocabulary knowledge. It is important to learn specialised verbs like advert, aver, assert and allude and to note the prepositions that follow them. This improves performance not only in fill in the blank questions but also in comprehension of formal passages.

Final Answer:
The correct completion is adverted, so the full sentence reads: He adverted to the problem of air pollution in his speech.