In 1973,at the Height of the Oil Shortage,a National Speed

In 1973,at the height of the oil shortage,a national speed limit of 55 miles per hour was imposed on the states by congressional legislation that threatened withdrawal of highway funds if state legislatures failed to lower allowable speeds.This is an example of encouraging state behavior through

A) hostage grants.
B) an unfunded mandate.
C) categorical grants-in-aid.
D) dual federalism.
E) layer cake federalism.