class is null When an object of class LimkeSak represcuts a cpty ack, its o so. We deal with ADTs on theee levels. On which level do we just nced to know oww to a. application (or user, client b, machine (or assembly) d. implemestation or concretc) we represent the attributes and fulfill the responsibilities of the ADT in how 37, We deal with ADTs on three levels. On which lervel do we deal with the now" questions, as a application (or user, client b. machine (or assembly) c. logical (or abstract) d. implementation for concrete as in 38. We deal with ADTs on three levels. On which level do we just deal with the "wha" question, what does the ADT model, what are its responsibilities, what is its interface? a application (or user, client) b. machine (or assembly) logical (or abstract) d. implementation (or concrete 39. The following sequence of operations essentially leaves a stack unchanged. pop followed by push pop followed by top c. push followed by top d. top followed by push a. b. Objects can represent both a. variables and constants b. classes and inheritance c. information and behavior d. methods and constructors 41. wi Within an object, actions are modeled using a. classes b. variables c. methods d. constants 42