Before you use any questions that may be freely available and discussed online, do perform the following checks to ensure that the quality of your GMAT preparation is not compromised in any way.
In the past, our students have reported that in many instances the free content that they have come across contains errors. Students have also found that in case of free Verbal questions that they got access to, they found the explanations unsatisfactory and were not convinced with the option given as the correct answer.
Unless you are sure of the quality and authenticity of such free GMAT preparatory material, it is safer to stick to officially published GMAT material only. Besides the Official GMAT Guide.(latest edition is the OG 2019 edition), books published by Kaplan GMAT, Princeton Review GMAT, Manhattan GMAT etc. are reliable sources of practice.