`N_2` and `O_2` are the two main greenhouse gases.

Answer

**Step-by-Step Solution:**

1. **Understanding Greenhouse Gases:**
- Greenhouse gases are gases present in the Earth's atmosphere that have the ability to trap heat. They play a crucial role in maintaining the Earth's temperature by allowing sunlight to enter the atmosphere while preventing some of the heat from escaping back into space.

2. **Identifying Common Greenhouse Gases:**
- The most common greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor (H2O). While nitrogen (N2) and oxygen (O2) are abundant in the atmosphere, they are not considered greenhouse gases because they do not significantly absorb and emit infrared radiation.

3. **Clarifying the Question:**
- The question states that N2 and O2 are the two main greenhouse gases. This is incorrect. The two main greenhouse gases that contribute significantly to the greenhouse effect are carbon dioxide (CO2) and methane (CH4).

4. **Conclusion:**
- Therefore, the correct answer to the question is that N2 and O2 are not the main greenhouse gases; instead, CO2 and methane are the primary greenhouse gases responsible for trapping heat in the atmosphere.