As I made several of such SCs with same outcome, from now I will apply the rule:
"singular noun" of "plural noun" that "plural verbs".[/quote]
I like your rule, since "that" introduces a "essential modifier" different than "which" for example, it means that we cannot "erase the middleman ie: of y", ie
The actions of my friend are not very wise ( erase "of my friend")
As a general rule of "X of Y" from a Manhattan Gmat
"if you can remove a phrase from the sentence ("of y") , and the sentence still makes sense, the phrase is likely a "middleman"
Experts please advise
time is not on my side