The correct answer to this open question is the following.
Although options are not included in this question, we can answer the following.
The important change in the Sun over the past four billion years is thought to be very important to understanding the climates of Venus, Earth, and Mars is "a gradual brightening with time."
Our solar system is wonderful. The Sun exerts a key influence on the planets that orbit the Sun. Solar flares create a great impact on the closer planets, including planet Earth. Our relationship with the Sun is absolute. Indeed, life on planet Earth depends on the Sun. Sun rays along one year determine the weather, among other factors on Earth, as well as the Sun and its gradual brightening with time, which has impacted the climate of Venus, and Mars.
