What does the term "invisible web" refer to?

the "invisible web" is a subscription service available only to libraries and schools.
the "invisible web" refers to a large portion of the web that regular search engines cannot find.
the "invisible web" is made of libraries that have scanned their books and put them online.
the "invisible web" is a database that can be accessed only through the library of congress.

Read the paragraph. theodore roosevelt was the greatest president because as a leader of the progressive party, he brought about much-needed social, political, and economic reform. one of his economic reforms was to break up many large business trusts. by doing so, he took economic power out of the hands of the wealthy and powerful corporations and placed it in the hands of the ordinary people. theodore roosevelt’s reform policies, known as the square deal, to give the average citizen an equal share of opportunities. which sentence is the thesis of this paragraph? theodore roosevelt was the greatest president because as a leader of the progressive party, he brought about much-needed social, political, and economic reforms. one of his economic reforms was to break up many large business trusts. by doing so, he took economic power out of the hands of the people and placed it in the hands of the ordinary people. theodore roosevelt’s reform policies, known as the square deal, to give the average citizen an equal share of opportunities.