A. because the 10th amendment gave states reserved powers.
The 10th Amendment of the United States Constitution establishes that powers not delegated to the federal government nor prohibited to the states by the Constitution are reserved to the states or to the people. This means that any powers not specifically granted to the federal government by the Constitution are reserved for the states, including the power to regulate intrastate commerce, provide for public safety, and establish local governments, among others. The reserved powers of the states are an essential part of the federal system of government in the United States, which divides power between the federal government and the states.