Look! That fellow is too sleepy to work. He ______ up reading until midnight.

A．mustn’t stay

B．mustn’t have stayed

C．ought not to stay

D．should not have stayed

合同当事人双方协议以新贷偿还旧贷，除保证人知道或应当知道者外，保证人不承担民事责任，新贷与旧贷系同一保证人的除外。 ( )