Based on the passage about exploring an underwater world with a mask and tube, select the correct answer to the question “How can one avoid the mask fogging up while viewing the sea life”.

Introduction / Context:
This question focuses on a specific instruction given in the passage about snorkelling. The instructor explains how to prevent the mask from fogging up while viewing the underwater world. Choosing the correct answer requires close reading and attention to detail. Such factual questions are common in reading comprehension sections and reward students who carefully note exact statements made by the author.

Given Data / Assumptions:
The passage clearly states the following:

• The instructor rules include the line: Breathe through your mouth, not your nose; else the mask will fog up.
• The writer describes finding it difficult at first but later getting used to this breathing pattern.
• The focus is on preventing fogging of the mask, not on swimming technique or direction of vision.
• The breathing instruction is the main practical step given in the text.

Concept / Approach:
The approach here is straightforward. We must locate the exact instruction related to mask fogging and then select the option that restates it correctly. The passage makes it clear that breathing through the mouth instead of the nose helps keep the mask clear. None of the other options are mentioned or implied in the passage. Therefore, only the option that refers to mouth breathing as instructed can be correct.

Step-by-Step Solution:
Step 1: Recall the instructor precise rule: Breathe through your mouth, not your nose; else the mask will fog up. Step 2: Understand that fogging occurs due to warm moist air from the nose entering the mask. Step 3: Look at option b, by breathing through the mouth as instructed. This matches the rule exactly. Step 4: Check option a, which mentions breathing through the nose and exhaling through the mouth. This conflicts with the passage, which warns against breathing through the nose. Step 5: Option c talks about keeping the head fully under water, which is not discussed as a method to prevent fogging. Step 6: Option d suggests looking downwards, again not mentioned in relation to fogging. Step 7: Conclude that option b is the only answer supported directly by the passage.

Verification / Alternative check:
As a verification step, you can re read the first lines of the passage, which clearly link breathing through the mouth with preventing fogging. The writer also comments on getting this wrong several times, emphasising that this specific rule is important. No alternative method is offered in the text. Therefore, any answer that does not speak of mouth breathing alone cannot be correct.

Why Other Options Are Wrong:
Option a is wrong because it includes breathing through the nose, which the passage explicitly warns against. Option c is incorrect as head position under water is unrelated to the mask fogging problem in the passage. Option d is wrong because looking downwards or in any direction does not affect internal condensation in the mask. These options may sound plausible in general, but they are not supported by the text and therefore must be rejected.

Common Pitfalls:
Some learners answer such questions based on their own guesses or outside knowledge rather than on the passage itself. Others misread the instruction and remember only that breathing was mentioned, without noticing that the nose must be avoided. A good habit is to always return to the relevant line in the passage and compare it word by word with the options, choosing only the one that accurately reflects what is stated.

Final Answer:
The mask can be kept from fogging up by breathing through the mouth as instructed.