The word 'plentiful' fits the context, indicating a large amount of pollution in the air, as described in the passage. Here's why the other options are incorrect:
- Option (a) 'Insufficient' suggests a lack of something, which contradicts the passage's idea of abundant pollution.
- Option (b) 'Pathetic' is a negative word, which doesn't fit the neutral descriptive tone used in the passage.
- Option (c) 'Meagre' implies something small or insufficient, which is opposite to the idea of large-scale pollution in the passage.
Thus, (d) 'Plentiful' is the correct choice.