What Is the Purpose of Block Grants or Federal Aid

What is the purpose of block grants or federal aid given to state or local governments?

A) It is to be divided into discrete "blocks" of grants, each limited to $100 million.
B) It is to be spent on a specific policy area decided on by the federal, state, and local governments.
C) It is to be spent in the way the state or local government decides to spend it.
D) It is to be tied to federal mandates that state or local governments must then implement or they will be taxed on the money.
E) It is to be contingent on state/local endorsement of so-called "social" federal legislation.