Welcome Susan. I've put together a memory card guide for the a7C that you might find helpful:
Find the best memory cards for shooting stills and video with the Sony a7C.
www.alphashooters.com
Basically if you shoot a lot of continuous bursts then it's best to go with a UHS-II card like the SanDisk Extreme Pro UHS-II (300/260).
If you don't shoot many continuous bursts then a UHS-I card like the SanDisk Extreme Pro UHS-I (170/90) will be perfectly fine.
There are benefits to the UHS-II cards when it comes to copying files over to your computer, as they will copy roughly twice as fast as the UHS-I cards if you are using a UHS-II card reader like the Sony MRW-S1.
Hope that helps!