Afghan refugees living in Iran to escape terrorism - Push factor
Bangladeshi migration to India due to flood - Push factor
Admission to university in England - Pull factor
Migration to Canada for a better lifestyle - Pull factor
Migration to America to escape religious persecution - Push factor
Entrepreneur moving to Singapore for a better business opportunity - pull factor
I would say D. Fossil fuels must be burned to release their energy.
The correct answer is - secondary economic activity.
The developing countries are trying to boost and develop their economies by developing the industry. They build lots of industrial facilities, factories, and instead of selling the raw materials to the more developed countries, they start to use the raw materials for their own purpose and manufacture them into products ready for the market. This production can include anything from creating steel from the iron ore, make juices from the fruits and vegetables, use the cotton for making clothes etc., so all in all making final products that directly end up on the market, thus making a bigger profit.
Even though it is slums we are talking about, and we know how terrible the conditions are, still there's always some surprises (negative ones unfortunately). Specifically in Mumbai, it is surprising that big portion of the people living in the slums do not have access to city services, they do not have enough water even thought the city itself is surrounded by water, more then half of the population of Mumbai lives in slums (around 55%), most of the residents do not have toilets and have to pay for public toilets...