The solution is immensely complex. (Singular subject + Singular verb)Originally Posted by jack
The solutions are immensely complex. (Plural subject + Plural verb)
The phrase 'to these problems' is made up of a preposition (to), a demonstrative (these) and a noun (plural). The entire phrase is called a prepositional phrase and it modifies the word 'solution'. That is, it tells us more information about the word 'solution'.
All the best,