Greenhouse Gas Emissions in the Agriculture Sector:
The greenhouse gas emissions from the agriculture sector contribute significantly to global warming and climate change. Different agricultural activities have varying levels of emissions. Let's arrange the given options in decreasing order of greenhouse gas emissions in the agriculture sector.

1. Livestock Product:
Livestock production, including cattle, sheep, and goats, is a major contributor to greenhouse gas emissions in the agriculture sector. Livestock emit methane through enteric fermentation, which is a natural digestive process in ruminant animals. Methane is a potent greenhouse gas, and livestock are responsible for a significant amount of global methane emissions.

2. Rice:
Rice cultivation is another significant source of greenhouse gas emissions in the agriculture sector. When rice paddies are flooded, anaerobic conditions are created, leading to the production of methane by bacteria in the soil. Methane emissions from rice cultivation contribute to a substantial portion of global methane emissions.

3. Cereals:
Cereal production, including crops like wheat, maize, and barley, also contributes to greenhouse gas emissions. The emissions mainly come from the use of synthetic fertilizers, which release nitrous oxide (N2O) during their production and application. Nitrous oxide is a potent greenhouse gas with a much higher warming potential than methane.

4. Pulses:
Pulses, such as lentils, chickpeas, and beans, have relatively lower greenhouse gas emissions compared to the other options. While they do contribute to emissions through agricultural practices, their overall emissions are lower due to their nitrogen-fixing ability. Pulses can fix atmospheric nitrogen, reducing the need for synthetic fertilizers and subsequently lowering emissions.

Therefore, the correct order of greenhouse gas emissions in the agriculture sector, from highest to lowest, is as follows:
3-1-2-4
- Livestock Product (3)
- Rice (1)
- Cereals (2)
- Pulses (4)

Livestock production has the highest emissions due to methane release, followed by rice cultivation and cereal production due to nitrous oxide emissions. Pulses have the lowest emissions in the given options due to their nitrogen-fixing ability.