The demographic transition consists of several stages: 

Pre-industrial stage: high death rates and high birth rates 

Transitional stage: death rates fall due to rising food production and better medical care. Birth rates remain high, so population surges. 

Industrial stage: birth rates fall, as women are employed and as children become less economically useful in an urban setting. Population growth rate declines. 

Post-industrial stage: birth and death rates remain low and stable; society enjoys fruits of industrialization without threat of runaway population growth. 

b (iii) We agree with the statement that vegetarians on average have a smaller ecological foot print because this reduces the meat production.

- Measures the amount of land and water used by an individual, a city, a country, a region, or all of humanity uses to produce the resources it consumes and to absorb the waste it generates with today's technology and resource management practices.

How to measure ecological footprint:
https://www.youtube.com/watch?v=MAKFdaJ3i3c

b(ii) relationship of EF and stage of demographic transition

Demographic transition is the model of economic and cultural change to explain declining death rates, declining birth rates, and rising life expectancies in Western nations as they became industrialized. The demographic transition consists with various stages, they are  Pre-industrial stage,  Transitional stage,  Industrial stage,  Post-industrial stage . The relationship between the ecological footprint and demographical transition is 

- They don't consume meat. Meat production requires to use much water to grow plants to feed the animals, and to give them drink. Crops to feed animals also use land. Therefore, someone who eat meat has a much larger footprint than a vegetarian.  

Waste absorption is part of EF. Landfill especially take large amount of land. Recycling allows to spare this land.