While Their Ability to Do So, or Ease of Doing

While their ability to do so, or ease of doing so, depends on their own statutes and constitutions, state legislatures may legally shift city limits and the boundaries of counties because:

A) the federal Constitution allows this, in suggesting that local governments are conveniences of states.
B) local governments are not mentioned in the federal Constitution, and as such are creatures or conveniences of the states.
C) power was returned to the states in recent decades, largely by Republican-dominated Congresses and presidents.
D) the regulation of local governments does not interfere with interstate commerce.