Thanks for helping. I think I misunderstood the instruction "Select a volume". I thought that had to be within the "options" choice. Actually in my case, only one volume is shown, and it's outside "options". I thought this was just a way of getting back to a normal restart. Perhaps the instruction should be clearer about what you see when you load startup options. Anyway, my mistake.
Incidentally, the issue that made me want to start in Safe Mode - an SD card that apparently couldn't be read on my MacBook Pro - solved itself after I'd moved the computer from France to England. It was probably some small item of dirt in the SD slot that was shaken out on the journey! Not all problems are software problems.