Answer:
Explanation:
You are perfectly correct to be confused. When you read the rules you have been given, none apply to this sentence. The problem is "longest." Longest is an superlative adjective (in this case). It can also be an adverb. But it is written as a subject which implies that it is a noun (which it is not).
If you turn the sentence around, you will see how it should be written to clear up the confusion.
The next group is the longest of the presentations.
Now you can see clearly what's going on. Group is the subject (and a noun) and there is a rule that covers it. The 6th rule that you have been given is that a word like group is to be considered singular even though many people belong to it. The correct verb (is) is also singular.
In my day, when dinosaurs were our next door neighbors, longest was termed a predicate adjective and of the presentations is an adverbial phrase.
Ain't grammar wonderful??!!?
