The Anabaptists a. opposed the practice of baptism. b. were not regarded as a political threat as they preached separation between church and state. c. were founded by Conrad Grebel, beginning as an elitist movement. d. advocated adult baptism, and if they had been baptized as children, a second baptism. e. peacefully merged with the Calvinists and Lutherans.

D. Advocated adult baptism, and if they had been baptized as children, a second baptism.

Explanation:

Anabaptists, were a christian grouped who had origins that can be traced back to the sixteenth century. They were of the belief that anyone who professes to be a christian must make a conscious decision to follow Christ. As a result of that, they rejected infant baptism. Anyone who converted to their religion would have to be baptized again even if they had been baptized before as infants.

Their system of belief was based on the teachings of Christ's Sermon on the Mount. So, they did not swear oaths, engage in war or even participate in politics.