ER 2 ?

In ER Excercise #2 the answer to question #1 states that advisor, which is the 1-M relationship between professor and student needs to be represented by a table, while position, which is the associative entity between professor and department does not need to be represented by a table. This seems contrary to our rule that M-M relationships, entity types, and associative entities are the only things we respresent as tables. Also, in the question #2, the answers say that a foreign key of professor needs to be embedded in the advisor table.