Solar flares can
a. knock out power grids.
b. be dangerous to astronauts.
c. disturb radio communications
d. all of these

d. all of these

Explanation:

If an enormous solar flare like the one that hit Earth a hundred or so years ago, years ago struck us today, it could knock out our electrical grids, satellite communications and the internet.  Very high-energy particles, can cause radiation poisoning to humans and other mammals. They would be very dangerous to unshielded astronauts. Luckily for us Earth's atmosphere and magnetosphere protect our human bodies from the effects of solar flares. Solar flares also release bursts of X-rays from the Sun that travel outwards in all directions as fast as the speed of light. Strong flares such as these can disrupt radio and aviation communications.

Hope this helps!!

answercoenzymes;