You will find online a lot of explanations about what is expected from you to do in this part of the GMAT test.
In my opinion you only need to have in mind a structure organized in paragraphs:
- State the both sides of the argument (you can use copy/paste from the text) and say which side you take.
- Write the first reason to support you argument.
- Write the second reason to support you argument.
- Write the third reason to support you argument.
- Write your conclusion which is also a reiteration of the last part from the first paragraph.
As an example:
- Admittedly … nevertheless …
- The main reason for my view …
- Another reason …
- Moreover …
- Therefore, I acknowledge that … nonetheless …
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[...] Paragraphs (as in the post about analysis of an issue): [...]