Fix placeholders

[svtk]

I've fixed the placeholders for Downcasting Task 1, thanks (in a different way, by showing the same code as in the referred sample as initial code), but don't see what's the problem with placeholders in Polymorphism Task 1. They seem to work for me.

[sofiiako]

don't see what's the problem with placeholders in Polymorphism Task 1. They seem to work for me.

@svtk maybe I was experiencing a plugin issue... sometimes it moves placeholders around