Scientists would predict that all of the following could happen due to solar flares:
- Radio navigation systems and global positioning systems will be inaccurate
- Electrical systems in satellites will fail
- Power grid operations will go offline
- High-frequency radio waves used for radio communication will be blocked
However, if you need to choose one option that represents a common consequence of solar flares, you could pick "high-frequency radio waves used for radio communication will be blocked." This is a direct and often observed impact of solar flares and their associated phenomena.