Why is a doubt about impurity in the public domain treated as pure?
Halacha 1: the Sages derive from the communal Paschal sacrifice that even definite impurity can be overridden publicly — making individual public-domain doubt certainly lenient.
Question 2
An impure child is found standing next to dough with dough on his hand. Is the dough impure?
Halacha 3: the presumption is that children pat dough — this constitutes a known behavioral pattern (chazakah), not just a doubt, making the dough presumed impure.
Question 3
A child holding flowers was found next to a cemetery, where flowers only grow in the impure area. Is the child impure?
Halacha 8 (halacha 7): the child is pure because of the doubt — another person may have gathered the flowers and given them to him. We follow the state at discovery.
Question 4
At what stage of development can one eat pure foods that touched a child's HANDS?
Halacha 10 (halacha 9): the fourth stage — when a child can guard his hands — allows pure foods that touched his hands to be eaten. The third stage (answering questions) only affects private-domain doubt rules.
Question 5
A donkey stands in a cemetery. Are the vessels on the donkey considered impure?
Halacha 8: the donkey has no capacity to respond to questions, and the vessels were found not touching the grave. Following the discovery-time principle, the vessels are pure.