The purpose of Schedule A is to let the organization indicate the reason as to why they are designated as a public charity, and the public support it receives. Tax-exempt organizations, nonexempt charitable trusts, and certain political organizations have to include this supplemental form Schedule A (Form 990 or 990-EZ.)
Generally, organizations will qualify under any one of the reasons listed under Part I Reason for Public Charity Status. However, if they fail to qualify in the subsequent sections Part II & III, then they are supposed to file Form 990-PF.
An organization has to check only one of the boxes in Part I of Schedule A even if it qualifies for more than one reason, and explains the reason for the remaining in Part VI of the Schedule A.
Note- The organization with Tax-exempt status 501(c)(3) and 4947(a)(1) must attach Schedule A