FOREIGN KEY constraint

Select all the correct statements about the tables schools and students that were created as follows:

CREATE TABLE schools (
 school_num INT PRIMARY KEY, 
 principal_name VARCHAR(40) NOT NULL, 
 city VARCHAR(25)
); 

CREATE TABLE students (
 first_name VARCHAR(20) NOT NULL, 
 last_name VARCHAR(20) NOT NULL, 
 school INT, 
 FOREIGN KEY (school) REFERENCES schools(school_num)
);