The Sentence Diagram Generator visually represents the grammatical structure of the sentence: "The world contains many countries that are extremely small."

1. Subject: The world

   • Determiner: The
   • Noun: world

2. Predicate: contains many countries that are extremely small

   • Verb: contains
   • Direct Object: many countries
     • Determiner: many
     • Noun: countries
     • Relative Clause: that are extremely small
       • Relative Pronoun: that
       • Verb: are
       • Adjective: extremely
       • Adjective: small

This structure can be visually represented in a diagram format, illustrating the relationships between the components of the sentence.