Figure 3.
(A) Grade 0, (B) Grade 1, (C) Grade 2, and (D) Grade 4.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.