In some cases, nouns can modify other nouns. When they do, remember that a modifying noun must be singular and is usually not possessive.
1. The car radio is one of the best on the market.
not: the cars radio... (or)
the car's radio...
2. This museum facility specializes in pre-Raphaelite drawings.
not: this museum's facility (or)
this museums facility
Yet, look at this one...
3. a. The student book is on the table.
A book made for the student, not the teacher, but a general book, not possessed by anyone.
b. The student's book is on the table.
A book possessed by an individual student.
c. The students' book is on the table.
A book possessed by a number of students.
Notice that the modifier will not change to agree with a singular or plural noun. It will always be singular, unless the noun-adjective is uniquely possessing the noun.