Introduction
If the elliptical orbit of the Earth around the Sun changes to a circular orbit, it would have various implications. Among the options provided, the correct answer is option 'D' - the difference between seasons may be changed. This means that the Earth's climate and the timing and intensity of seasons would be affected if the orbit becomes circular.

Explanation
Changing the elliptical orbit of the Earth to a circular orbit would have significant consequences for the planet. Let's explore the implications in detail:

1. Impact on Seasons:
- Currently, the Earth's elliptical orbit causes variations in the distance between the Earth and the Sun. This variation influences the amount of solar energy received by the Earth, leading to the different seasons.
- If the orbit were to become circular, the distance between the Earth and the Sun would remain constant throughout the year. Consequently, the variations in solar energy received by different parts of the Earth would be reduced.
- This would result in a decrease in the intensity of seasons. The temperature differences between summer and winter would be less pronounced, leading to milder and more consistent weather patterns.

2. Atmospheric Effects:
- The change in orbit would have an impact on the Earth's atmosphere. The current elliptical orbit causes variations in the distribution of solar energy, which drive atmospheric circulation patterns.
- If the orbit were to become circular, these circulation patterns would be altered. This could affect weather systems, wind patterns, and precipitation distribution across the globe.
- However, it is important to note that the exact atmospheric changes resulting from a shift to a circular orbit are complex and would depend on various factors, including the Earth's atmospheric composition and the redistribution of heat.

3. Other Factors:
- While the change in orbit would primarily affect the seasons and atmospheric dynamics, it would not cause all gases on Earth to escape (option B). The Earth's gravity would still be sufficient to retain the atmosphere.
- Similarly, the sudden cooling and uninhabitability of the Earth (option C) is unlikely solely due to a change in orbit. The habitability of a planet depends on a complex interplay of various factors beyond just its orbit, such as the presence of water, greenhouse gases, and the composition of the atmosphere.
- Option A, stating that it would not make any difference to Earth, its atmosphere, and temperature, is incorrect. A shift from an elliptical to a circular orbit would indeed have significant effects on climate and seasons, as explained above.

Conclusion
Changing the elliptical orbit of the Earth to a circular orbit would result in a change in the difference between seasons. This would lead to milder and more consistent weather patterns, with reduced temperature variations between summer and winter. Additionally, the shift in orbit would have implications for atmospheric dynamics, affecting weather systems and circulation patterns. However, it is important to note that the habitability of the Earth and the retention of its atmosphere would not be significantly impacted by this change.