Most in need of an isolating valve, bidet or toilet?

According to this practice question, the bidet is most in need of an isolating valve:

But not according to this practice question:

They are obviously two different questions with two different conclusions. The first deals with cross contamination of the potable water supply, and the second merely with wasting water (constant running). Instead of dissecting every question - you merely need to provide the BEST answer.

That’s exactly why I’m requesting help from this forum. It just seemed logical that the device most at risk of cross contamination should have an isolation valve.

Bidet is not a choice in the question that references an isolation valve. You do realize that an isolation valve merely turns the water to a fixture or device off so that it can be serviced.

Sure it is.

Oh, I was thinking back-flow preventer. My mistake. That makes more sense now.