Recall that the Earth's axis is tilted which actually changes the angle of sunlight that strikes the Earth and this is the reason why we have different seasons.
If the angle of Earth's axis decreases, there would be less extreme seasons meaning that the summer season would be cooler and the winter season would be warmer.
Looking at the options, only option d is correct.
"If the angle of Earth's axis decreases, winters would be warmer"
