why does "blend" not work here?

 From:  mike (MIOHN)
4993.1 
Hi,

sorry again!

I cannot blend that curves. Why?

I always have problems with differencation of "construction" splines
and "work" splines. Which are which? And which can I delete after f.e. trimming?

And so often I use the "joint/verbinden" command and then
I still can select the individual splines. So they did not joint. I cannot understand that.
I merge and merge and merge and still have single items.

???

regards
MIke
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