Could this be a thesis statement at the end of the paragraph? Not really because it doesn't point to a solution. It just leaves us hanging there contemplating the problem. This is not the right place for this sentence.

Sentence Two

Correct. A problem was outlined in sentences 1 and 2. And now we have a solution - or rather a pointer to a solution, which we would expect to find in the rest of the text. Final sentences in paragraphs often point forward to the next paragraph or something later in the text. And they often indicate the type of information you might find such as a solution (as here), further examples or evidence, constrasting opinions or evidence), and so on.

Modern life is full of distractions – and some of them can have a negative effect on our ability to concentrate when studying.

If this is not the last sentence in the paragraph, you'd expect it to be followed by a summary of what you can do to get the most from your studies, or perhaps some advice like "Read it carefully.". But we don't have anything like that in these sentences so this is not sentence 2.

This paragraph was taken from an article entitled How to avoid distractions while studying, according to science in The Conversation (Vasilev, n.d.) and you can find the reference and link on the credits page.

Sentence Three

The problem is that many people tend to underestimate how much they are distracted by what’s going on around them.

Correct. But this is not really a classic topic sentence. It sets up the (negative) situation which the article seeks to resolve.

Here’s how you can get the most from your studies by considering your environment.

Comment This article from which this paragraph was taken is a problem solution text. And the introductory paraphraph is a kind of problem-solution abstract of the whole text. The problem, introduced and defined in the first two sentences, is further discussed in the next eight paragraphs (most of the text). The solutions are discussed in the last two paragraphs. To read the whole article, find the reference from the information below and click on the link.

"The problem" at the beginning of this sentence refers to something already mentioned in the text. So this cannot be the first sentence.

A sentence like this could only be found at the end of a paragraph if it were at the end of a summary or conclusion. This is not the case here.

A sentence like this might be found in the middle of a longer paragraph (you might expect it to be followed by a list of different types of distraction, for example) but it doesn't fit well here. There are no references to anything which might be found previously in the text.

Correct. Having introduced the topic in the first sentence, this sentence clearly identifies a problem (people underestimating how much they are distracted ...). So a problem is introduced in the first sentence (negative effect on our ability to concentrate) and defined in this one.

Sentence One

"Here's how....." introduces some advice. We can imagine what that might be since we know the title of the article. There is no advice in any of these three sentences, so this sentence is not sentence 1.

D1 Occupied

D3 Position

D1

false

D0

D2 Occupied

D1 Position

D2 Position

D2

Comment This is some comment about the text. This is some more comment about the text.

D3

D3 Occupied

1The Histories by Herodotus (484BC to 425BC) offers a remarkable window into the world as it was known to the ancient Greeks in the mid fifth century BC. 

3 This sets the baseline for the remarkable advances in their understanding over the next few centuries – simply relying on what they could observe with their own eyes.

2 Almost as interesting as what they knew, however, is what they did not know.