I forgot to include the following sentences. Thank you very much for your help.

1) The man thinks that that gang of teenagers back there is an absolute disgrace.
2) He believes that in a town that size there should be more for young people than just hang around the railway station. Though they are harmless, it just infuriates him to see that they have nowhere to go. (What infuriates him the most about them is that they have nowhere to go: can you say it that way?).
3) Margaret Mears points out that there are thousands of places where animals are still suffering, though it is not necessary.
4) She believes there are alternatives to using live animals to test cosmetics and drugs.
5) Unfortunately governments don’t always see it as a big issue (how can I rephrase it?) so she needs the support, above all the donations of ordinary people to help her organisation to carry on.

1) The man thinks that that gang of teenagers back there is an absolute disgrace.

The man thinks that the gang of teenagers back there are an absolute disgrace.

I wouldn't use gang though--I would just say group of teenagers.

2) He believes that in a town that size there should be more for young people than just hang around the railway station. Though they are harmless, it just infuriates him to see that they have nowhere to go. (What infuriates him the most about them is that they have nowhere to go: can you say it that way?).

Your first sentence doesn't really make sense.- I seriously do not understand what you're trying to say.

3) Margaret Mears points out that there are thousands of places where animals are still suffering, though it is not necessary.

That is good in the starting, but I don't like the ending....though it is not necessary.

4) She believes there are alternatives to using live animals to test cosmetics and drugs.

Try to fix this sentence.

5) Unfortunately governments don’t always see it as a big issue (how can I rephrase it?) so she needs the support, above all the donations of ordinary people to help her organisation to carry on.

Governments don't always see donations going towards ordinary people as big issues.

Can you take it on from there.

Please post back after you've made your corrections. I'd be more than happy to check them over again.

1) The man is expressing his opinion that the gang of teenagers behind him is very disgraceful.

To determine what infuriates him the most about the gang, we look for the relevant information in the given context.
In the provided sentences, it is mentioned that "it just infuriates him to see that they have nowhere to go." So, what infuriates him the most about the gang is their lack of a place to go.

2) The man believes that in a town of that size, there should be more recreational options for young people rather than just loitering around the railway station. Although they are harmless, their lack of other activities frustrates him.
To rephrase "What infuriates him the most about them is that they have nowhere to go," you can say "Their lack of a suitable place to go is the primary source of his frustration."

3) According to Margaret Mears, there are numerous instances where animals continue to suffer needlessly.
To find appropriate alternatives for using animals in cosmetics and drug testing, you can refer to Margaret Mears' suggestions or research other sources that provide information on alternative methods.

4) Margaret Mears argues that there are viable substitutes for using live animals in cosmetic and drug testing.
Here, you can either rely on Margaret Mears' specific alternatives or seek additional information on alternative practices.

5) Regrettably, governments do not always perceive it as a significant issue.
To express this idea differently, you can say "Unfortunately, governments do not always consider it a matter of great importance."