Hi Sandeep,
You can focus on "all of the supplements" and the confounding factors addressed in the majority of the main analyses. As mentioned in response to Jean's question, please be sure to address the residual confounding question and anything you'd do to improve the study with regards to bias due to confounding.
You are welcome to also critique or comment on the beta-carotene specific analyses if you wish, or if this is part of your topic that you would "improve".
Hope that clarifies.
best,
June