Answer:
a. solar radiation
Step-by-step explanation:
The magnetosphere is the region of space around the Earth where its magnetic field is predominant, than the field of other bodies. The magnetosphere has constanly interaction with the solar wind.
An important function of the magnetosphere is that it works a shield, this magnetic field is strong enough to help us against solar radiation, that means if the Earth doesn't have the magnetosphere, life wouldn't be possible on Earth.
Therefore, the right answer is a.