Cpr must be performed if these conditions exist: unconsciousness and no breathing and/or no pulse.
a. true
b. false

True. If you look at when doctors do CPR, they usually perform CPR when there is no breathing and/or no pulse. Think of CPAP machines. They force air into the lungs when someone stops breathing in their sleep (sleep apnea). Hopefully this did not confuse you.

Awould be the most dangerous

Blood transfusions were rarely done and often fatal; they were outlawed until the nineteenth century.