I am trying to register those sites, but they ask you a number of questions like
Butterfly in the...:
I can go twice as...:
Take a...:
It's in a...:
A Reading...:

But can't find where to answer those.

Copy/paste and use a search engine. The whole thing, not line by line. You'll get it.

Just trying to avoid bots over there, and this one has had the best success rate so far.

If you're just looking to download stuff at Insim, you don't need an account since everything should be accessible (but IA, not so much). The activity level is at an all-time low at Insim (no idea about IA), so don't expect too much.

I feel old. I guess Reading Rainbow isn't a thing anymore?

I'm not American, so never heard of it before, and had absolutely no idea what it was (but found the answer to the riddle after one or two searches back when someone started complaining how difficult this one was, 'cause I got curious). Not everything American gets translated to the rest of the world, although wouldn't mind a version of this one to some of the weird junk they put on kids' TV these days.

Looks like it was cancelled a while back. This one ought to come back, because it does look like a good concept.

That's true, I forgot about international users. For context, Reading Rainbow was a popular program on PBS (Public Broadcasting Service). And, given how prevalent tv is among Americans, almost every kid of a certain age has heard of the show, or watched it at one point in their lives. Before streaming, and back in the early days of cable, there wasn't a ton of kids programming and some programming, like Disney, was restricted to cable. So if you were a kid watching tv in the middle of the day, you'd be watching at least some PBS. Reading Rainbow was one of the programs meant to encourage reading; when I was a kid, it aired right after Learn to Read, iirc.

So yeah, for Americans it's widely known, but I guess maybe not as popular as some of the other PBS staples like Sesame Street, Barney, Arthur, etc. It's almost like how most 90s kids could probably sing along to the original Pokemon theme or how girls in that same age range all seem to know the Sailor Moon theme song. Arthur was another popular theme, too, actually. It's a little weird how with streaming now, people aren't always in tune to the same things. That sense of shared culture is now different, even in the same country. Anywho, nostalgia lane trip over.