Each one is correct except d
The correct answer is - oxygen.
The phytoplankton and the microscopic marine plants are using the process of photosynthesis in order to produce energy for them. In order for this process to take place, two things are needed, sunlight and carbon dioxide. The consumed carbon dioxide is not totally used, but there's some waste from it. The waste is actually the oxygen. The oxygen is released and it gets back into the atmosphere. This gas is crucial for the survival of the living organisms on the planet, especially the animals, so it is extremely import that the environment of the phytoplankton and the microscopic marine plants is not destroyed, as they are the ones that release the biggest amount of oxygen into the atmosphere.
Air travel is usually the largest component of the carbon footprint of frequent flyers. A single return flight from London to New York – including the complicated effects on the high atmosphere – contributes to almost a quarter of the average person’s annual emissions. The easiest way to make a big difference is to go by train or not take as many flights.
2 The second most important lifestyle change is to eat less meat, with particular emphasis on meals containing beef and lamb. Cows and sheep emit large quantities of methane, a powerful global warming gas. A vegan diet might make as much as a 20% difference to your overall carbon impact but simply cutting out beef will deliver a significant benefit on its own.
The person would be unable to fully digest dairy products
