In the following question, the sentence is given with a blank to be filled in with an appropriate word. Select the correct alternative out of the four: Teach them that taking a few precautionary measures to prevent infections and diseases is _____.

Introduction / Context:
This final blank in the hygiene passage summarises how important it is to take precautionary measures. The preceding text talks about children being vulnerable to hygiene-related disorders and the need to teach them what to avoid and what actions to take. The missing word must convey a sense of strong necessity, not something casual or optional.

Given Data / Assumptions:

• Sentence fragment: “Teach them that taking a few precautionary measures to prevent infections and diseases is _____.”
• Options: optional, secondary, voluntary, imperative.
• The passage promotes hygiene and disease prevention as serious matters.
• We must select the adjective that best expresses strong obligation or essential importance.

Concept / Approach:
The word imperative means absolutely necessary, vital or of great importance. In health communication, it is common to say that something is imperative when it must be done to protect health. Optional means something you may choose to do, secondary means less important than something else, and voluntary means done by free choice rather than obligation. None of these alternatives match the urgent, must do tone of the sentence.

Step-by-Step Solution:
Read the sentence with “optional”: that would imply that precautionary measures need not be taken, which contradicts the message of the passage.Read with “secondary”: this suggests that these measures are of lower importance than some other concern, which again conflicts with the stress on prevention.Read with “voluntary”: this describes whether an action is forced, not its importance, and does not capture the sense of necessity.Read with “imperative”: “is imperative” clearly means that it is crucial and must be done, aligning perfectly with the tone of health advice.Therefore, imperative is the best and most precise choice.

Verification / Alternative check:
Insert the chosen word into the full passage: “Teach them that taking a few precautionary measures to prevent infections and diseases is imperative.” This reads exactly like advice from a doctor or health expert and reinforces the idea that such measures are not negotiable luxuries but essential steps.

Why Other Options Are Wrong:
Optional undermines the seriousness of the advice by suggesting that skipping these measures is acceptable. Secondary downplays their importance, as if there were more urgent matters than preventing disease. Voluntary simply indicates that nobody is forcing them by law and does not say anything about the recommended level of importance. Only imperative communicates the required sense of key importance and urgency.

Common Pitfalls:
Students sometimes confuse voluntary with important, assuming that voluntary acts are always good or desirable. In vocabulary based blanks, always match the word to the exact nuance of the sentence. Here, the focus is on how necessary the actions are, not on whether they are freely chosen. Remember that imperative is a strong word used whenever something is extremely important and must not be neglected.

Final Answer:
The blank should be filled with imperative, making the sentence, “taking a few precautionary measures to prevent infections and diseases is imperative.”