Answer: I’m working to save up for some new music.
Denise likes to get her exercise by dancing.
Dave has to walk the dog every morning.
Step-by-step explanation:
The infinitive in English expresses the meaning of the verb in a general way, without reference to any verbal tense.
As a rule in English grammar, when a verb is in infinitive it must be preceded by the particle 'to', for example, 'to play'.
According to this explanation, only the following sentences contain an infinitive:
I’m working to save up for some new music.
Denise likes to get her exercise by dancing.
Dave has to walk the dog every morning.
The other sentences, although have the particle 'to' are not followed by a verb.