I bumped into that quiz, and I'm quite confused by these two questions' answers. I would appreciate any clarifications.
A) Jane talks on the phone. Bob has been talking on the phone for an hour. Mary is talking on the phone. Who is not necessarily on the phone now?
For my understanding, there is a chance that also Bob is not necessarily on the phone, due to the use of the Present Perfect Continuous.
One of the uses (source) of the tense is for Finished actions - Actions which have recently stopped (though the whole action can be unfinished) and have a result, which we can often see, hear, or feel, in the present. We don't use a time word here. Eg. "I'm so tired, I've been studying."
B) I'm going to make dinner for Frank. I'm making dinner for Judy. I'll make dinner for Mary. I make dinner for Ted. I will be making dinner for Tony.
Who are you offering to make dinner for?
Is it absolutely wrong to say that I'm offering to make dinner to Frank? My friend told me that it sounds natural for him in the given context. I do get that the question is about the differences between "I will" and "Going to"