An example of a reserved power to the states by the 10th amendment is the power to
a. make foreign treaties
b. admit new states to the union
c. establish and support public schools
d. build and run a post office

c. establish and support public schools

Explanation:

According to this amendment, the US Constitution does not fix state jurisdictions, but retains residual competence, that is, issues and problems that are not within the jurisdiction of the federation and are not included as special prohibitions. This principle of residual competence is one of the two main components of the principle of federalism enshrined in the US Constitution. Section 8 of Section I of the US Constitution contains an exhaustive list of jurisdictions delegated to the federation and held solely by Congress (setting federal taxes, minting, making foreign treaties, admitting new states to the union, setting up courts, etc.). Issues of legislative regulation not mentioned in this section, with some reservations, relate to state jurisdiction, which was clarified in 1791 by the 10th amendment.  

The kind of plan schools offer is directly dependent on the instructions of the city department of education and the preferences of the government of each particular state. There is no a single law on education, and there is even no a single school curriculum in the United States. The government gave the reins of school education to the states, each of which has a department of education with its own idea of schools.

(C) Establish and support public schools

Explanation:

The Tenth Amendment may itself represent a substantive point of confinement on assumedly conceded forces. Regardless of whether present-day improvements license extension of congressional position well past its eighteenth-century limits, such development cannot douse the "held role" of the states as restricted, however independent sovereigns. The Tenth Amendment, therefore, may work as a kind of instrument: Congress has full capacity to manage, and even to expose states to commonly relevant government laws, yet the power closes when it ventures excessively far into the held territory of state self-sufficiency.

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