Our answer:

S	P	C
The little professor's habit (of wearing bow ties) |	is getting |	a bit boring

Here 'of wearing bow ties' is a clause beginning with the preposition 'of' and which has a PO structure. It is part of the Subject NP, and clearly postmodifies 'habit'. But it is not a relative clause - you can't insert a relative pronoun at the beginning of it. Because it begins with a preposition, we call, it a Prepositional clause (PCl). Another difference between RCls and PCls is that RCls can only act as modifiers inside NPs, but PCls can also act as modifiers in AdjPs or AdvPs.

Note, that PCls can be directly nested (see Task A) or indirectly nested (as here).

Next: Task E - indirectly nested clauses (iii) - comparative clauses (CCls)