Express these system specifications using the propositions p "The user enters a valid password," q "Access is granted," and r "The user has paid the subscription fee" and logical connectives (including negations). a. "The user has paid the subscription fee, but does not enter a valid password."
b. "Access is granted whenever the user has paid the subscription fee and enters a valid password."
c. "Access is denied if the user has not paid the subscription fee."
d. "If the user has not entered a valid password but has paid the subscription fee, then access is granted."