I recently wrote a sentence similar to the following one in a scientific context:
They are more similar to real-word problems, which [make / makes] them ideal benchmark domains.
I initially used the singular form "makes", because I thought "which" relates to the whole main sentence (i.e. "the fact" (it) that they are more similar to [...]). However, my supervisor told me it should be the plural form (make), because it relates to "problems". With German being my mother language, I find this odd, as we use the singular form in this case.
Which of the two versions is correct?