Consider the view that we need to radically change the way we eat if we are serious about saving the planet.
Whenever considering the concept of necessity, one (fairly) standard, solid argument against the idea of necessity is that of the presence of alternatives, discussed in this post.
With this in mind, for this question, one could argue that we do not need to radically change the way we eat if we are serious about saving the planet because there are viable alternatives – GM food designed to be environmentally friendly, hydroponics, vertical farms, etc.
The question above includes the term “need”. Similar key terms would be terms like “must”, “essential”, “crucial”, “important”, etc. Of these key terms, the most common one that Cambridge asks is “important”. For some (not all) of those questions, the same arguments for “necessity” could be used.
Questions where you could use “necessity” arguments:
How important is a sense of history in shaping the future of Singapore’s society?
Discuss the importance of religion in society today.
Questions where you might find it difficult to use “necessity” arguments:
How important are dreams?
Questions where you definitely can’t use “necessity” arguments:
To what extent do the newspapers and magazines that you read deal with what is trivial, rather than with what is important? (2006)
(For a complete list of questions, see these two pages  , and Ctrl+f to locate the term “important” or similar terms)