In the following question, out of the four alternatives, select the alternative which best expresses the meaning of the idiom or phrase. To go off the air.

Introduction / Context:
This question checks understanding of the English idiom to go off the air. Idioms are fixed expressions whose meanings cannot always be guessed from the literal meanings of the individual words. This particular idiom appears frequently in contexts involving radio and television. Examinations often include such phrases to test whether the learner is familiar with common media related expressions in modern English.

Given Data / Assumptions:

• The idiom is to go off the air.
• The options give several possible meanings, some literal and some related to broadcasting.
• The phrase is commonly used with radio and television channels.
• We assume the exam expects the standard idiomatic meaning used in media reports.
• The correct answer should relate to the idea of stopping or ending a broadcast.

Concept / Approach:
The phrase on the air refers to a programme that is currently being broadcast live or is in transmission. Therefore, to go on the air means to start broadcasting. By contrast, to go off the air naturally means to stop broadcasting or to end the transmission. The method here is to recall how the phrase is used in real news or announcements and match that usage with the closest option. Options that talk about food, medical ventilators, or travel are clearly unrelated to this media context.

Step-by-Step Solution:
Step 1: Recall that broadcasters say We are on the air to indicate that a programme is live. Step 2: Understand that if a station or show goes off the air, it stops broadcasting, either temporarily or permanently. Step 3: Examine Option C, which explains the idiom as to stop broadcasting a radio or television programme. Step 4: Notice that this exactly matches the media based understanding of the phrase. Step 5: Option A about removing a ventilator relates to hospital care, not to broadcasting. Step 6: Option B about not eating food for a long period has no connection with being on the airwaves. Step 7: Option D about wasting time on silly things is another unrelated everyday phrase. Step 8: Option E about travelling by aeroplane introduces a new meaning for air, but idiomatically to go off the air does not describe flying. Step 9: Conclude that Option C is the only correct interpretation.

Verification / Alternative check:
Consider an example announcement: Due to technical problems, the channel went off the air for two hours. In this sentence, the only plausible interpretation is that the channel stopped broadcasting for that period. None of the alternative meanings involving food or medical devices fit into such a statement. This contextual test confirms that the idiomatic meaning is related to stopping a broadcast, exactly as given in Option C.

Why Other Options Are Wrong:
To remove the ventilator of a patient on his death bed is incorrect because the expression off the air does not appear in medical terminology in that sense. To not eat food for a very long period is an attempt to link air with breathing or fasting, but English does not use off the air to describe fasting. To waste time on silly or trivial activities refers to killing time or fooling around, not going off the air. To travel by aeroplane for the first time confuses air with air travel, but again, this is not how the idiom is used in real life.

Common Pitfalls:
A frequent pitfall in idiom questions is to interpret the phrase word by word rather than as a fixed unit. Learners may also be distracted by options that have strong emotional content, such as a patient on his death bed, even though they do not match the typical usage environment of the idiom. The best approach is to recall or imagine sentences where native speakers would use the phrase and then test which option fits naturally in that setting.

Final Answer:
The correct answer is To stop broadcasting a radio or television programme.