Please explain the difference between these adverbs!

[Daisy]

Thank you, Mister Micawber. :D

I've got another question which comes from the textbook I'm using for teaching.

She nodded and shook her head at the right places. ___she understood what the philosopher was talking about.

There are several words to be chosen from: Certainly, Perhaps, Presumably, Surely, Undoubtedly. The correct answers that are give are Undoubtedly and Presumably.

But the students think that the other ones also fit here.
Since the sentence doesn't have any context, I really don't know how to explain it. And could you help me?

[Alan]

Hi Daisy,

I'd like to say that I don't think this is a very useful exercise if there is little indication of what the missing word (adverb) is. I say this cautiously because I could easily be open to a similar criticism about the 300+ tests I've already written for this site but I do think there should be some hint about the missing word. The reference to nodding and shaking of the head doesn't help much because she could be understanding or not understanding. That aside, I would have thought you could insert perhaps or presumably in the sense of I imagine/I think. Undoubtedly doesn't work for me because there is no indication that yes she did understand since we don't know what the nods and shakes signify. Surely and certainly don't work here for me either because they need to be linked to the first sentence somehow rather than float around unconnected, the same in my view applies to undoubtedly. If I were teaching in this case, I would give clear and separate examples of how each adverb is used with illustrative sentences and then apply this knowledge to the exercise in question.

Hope this helps

Alan
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English as a Second Language
You can read my ESL story Present Simple