Are you alone? Pfel war schlecht。 Einer in the sentence is a demonstrative pronoun: einer = ein Apfel (masculine, singular first case), der? Pfel is the second plural noun, so einer? der？ Pfel is equivalent to ein Apfel? der？ One of many apples.

In Cochines' room. Den Reis is the object of the case, so the fourth den is used. In German, when expressing a request, demand or explanation for something (such as a menu or product description), verb prototype phrases are often used instead of complete sentences.

I wish you a happy study!