The main focus of the passage is on :

Concept: The main focus — the central idea — of a passage is the theme that governs the whole text: the idea its paragraphs keep defining, prescribing, illustrating and returning to. A supporting detail, by contrast, is introduced in service of that theme in one part of the text, however striking that part may be. To identify the main focus, follow the organising thread rather than the most memorable sentence.

Application: tracing how this passage is organised, paragraph by paragraph:

1. It opens with the problem: climate change is 'one of the most serious threats to sustainable development', and vulnerability to it is not only geographical but also social, economic and political, so poor communities are hit hardest.

2. It then states its purpose — 'It is vital that these communities are helped to adapt to the changing dynamics of nature' — and immediately defines adaptation as 'a process through which societies make themselves better able to cope with an uncertain future'.

3. It sets out what adapting involves: sea defences, flood-proof houses on stilts, reduced water use in droughts, early warning systems, better water management, improved risk management, insurance options and biodiversity conservation.

4. It argues urgency and scale: the vulnerability of developing countries must be reduced, their adaptive capacity increased, national adaptation plans implemented, and adjustments made 'at every level from community to national and international'.

5. It closes on the resources for adapting: community resilience, appropriate technologies, traditional knowledge, and local coping strategies, called 'an important element of planning for adaptation'.

Every paragraph after the opening either defines the process of adapting, prescribes it, or supplies its means; the word adaptation and its cognates recur from the middle of the passage to its last line. That recurring, organising thread is what the passage is mainly about: adaptation to climate change.

Cross-check: the other themes named in the options each sit inside that structure rather than governing it —

• Social dimensions of climate change: raised once, near the start, to explain who is most vulnerable and therefore who must be helped.

• Combining traditional knowledge with appropriate technology: introduced late, as one means by which communities build resilience — a method of adapting.

• Co-ordination between regional and national efforts: appears as the scale at which adaptation must be planned, not as the subject the passage develops.

Result: the main focus of the passage is adaptation to climate change.