The sources of methane, a major greenhouse gas, among the given options are:

1. Rice fields: Option 1 states that rice fields are a source of methane, and this is correct. Rice cultivation involves a process called anaerobic decomposition, which occurs when rice paddies are flooded. In these anaerobic conditions, microorganisms break down organic matter and produce methane as a byproduct. Methane emissions from rice fields contribute significantly to the overall greenhouse gas emissions.

2. Coal mining: Option 2 states that coal mining is a source of methane, and this is also correct. Methane is often trapped within coal seams, and when coal is mined, the methane can be released into the atmosphere. Methane emissions from coal mining can occur during the mining process and also from abandoned or poorly managed coal mines. Methane released from coal mining activities contributes to greenhouse gas emissions.

3. Domestic animals: Option 2 states that domestic animals are a source of methane, and this is true as well. Livestock, such as cattle, sheep, and goats, produce methane as part of their digestive process. Methane is produced in the rumen, a part of the animal`s stomach, during the fermentation of food. The methane is then released through belching and flatulence. The global livestock sector is a significant contributor to methane emissions.

4. Wetlands: Option 1 states that wetlands are a source of methane, and this is also correct. Wetlands, such as swamps and marshes, are natural sources of methane. Methane is produced in wetland ecosystems through the anaerobic decomposition of organic matter by microorganisms. The decomposition process occurs in waterlogged conditions, where oxygen is limited. Wetlands can release substantial amounts of methane into the atmosphere.

Based on the above explanations, the correct answer is Option 4: 1, 2, 3, and 4. All four of the mentioned sources (rice fields, coal mining, domestic animals, and wetlands) contribute to methane emissions, making them significant sources of this greenhouse gas.