Answer is contrary to my test-out experience:

Ah, well - Errare humanum est.

So simple. Amazing 32% can get it wrong!

Ah, well - R is even nerdier than you think!

Oh, so tricky - but I got it right by testing out.
Still, it seemed inelegant, and I felt option 3 might be the intended right answer, as I...

... except given code doesn't run when R is case sensitive.

Still, it's deprecated?! https://docs.microsoft.com/en-us/sql/relational-databases/system-stored-procedures/sp-bindrule-transact-sql
You are encouraged to use Constraints instead!
/morten lintrup

Really interesting Q with a very instructive A - thank you!

Weird, but instructive - thank you!

Extend function is not known to my RStudio / RGui. An error to that effect is returned.

Didn't get it - don't understand the explanation.

A classic example of a multiple choice Q. easily answered by sheer psychology. One need only make a simple mental plot of how options relate to each other to see...

I see no essential difference between a heat map and a 2D contour plot. As in e.g. https://se.mathworks.com/matlabcentral/answers/152662-creating-a-simple-contour-plot-heat-map?

Oh, what a deceptive way to present the answer list, switching options 2 and 4, ...

Tried it out. Did not work as "correct" answer says. Likely because my test table had the clustered index defined non-unique. Confused question.