"To stem" is an infinitive. When an adverb is placed between "to" and "stem", it creates a split infinitive. A split infinitive is not a part of speech but a highly controversial grammar issue. Star Trek's "to boldly go. . ." is, perhaps, the most famous split infinitive.
It is called a split infinitive, but a split infinitive isn't one of the parts of speech.
Examples of split infinitives:
to quickly run
to generously sprinkle
Adverb.
The word 'when' can function as both an adverb and a conjunction. As an adverb, it modifies a verb, adjective, or adverb, indicating the time at which an action occurs. As a conjunction, it connects two clauses, indicating a specific point in time or an event that triggers another action.
Secretly is an adverb.
Nonetheless is an adverb.
It is an adverb
The word frequent is an adjective. It describes something that occurs often.
adverb
Between is a preposition and an adverb.
The word annual is an adjective. Example: we are having our annual meeting.
"Ever" is an adverb.
The word meanwhile is an adverb. It is the time between events.
The word 'when' can function as both an adverb and a conjunction. As an adverb, it modifies a verb, adjective, or adverb, indicating the time at which an action occurs. As a conjunction, it connects two clauses, indicating a specific point in time or an event that triggers another action.
Softly is an adverb.
The adverb for introduced is speech or talk it out
adverb
Secretly is an adverb.
It is an adverb