Answer:
D. Unitarianism was less strict and rigid than Puritanism.
Step-by-step explanation:
The best-supported inference about Unitarianism from the given text is D. Unitarianism was less strict and rigid than Puritanism. The text mentions that Unitarianism was a theological movement that emerged during the 18th century as a reaction against the rigid orthodoxy of Puritanism. The Unitarians rejected the Puritan emphasis on original sin and predestination and instead emphasized the essential goodness of human nature and the power of reason. This suggests that Unitarianism was indeed less strict and rigid than Puritanism. The text does not provide evidence to support options A, B, or C.