Which of the following is an example of a holding company? a railroad company buys its competitors' companies leaders from different transport companies agree to charge the same prices a company owns stock in several different corporations a paper factory owns a lumber yard and paper mill

A holding is a type of corporation does not provide goods or services, but simply owns stock from other companies in order to constitute a corporate group. It is a manner of reducing risk for investors/owners.

The other definitions provided correspond to the following phenomena:

absortion and monopoly: a railroad company buys its competitors'
collusive oligopoly: companies leaders from different transport companies agree to charge the same prices
vertical integration: a paper factory owns a lumber yard and paper mill