Is it a good design in RDBMS to reference RelationshipTable ID from another table

Question

Consider the following example

CREATE TABLE courses (
    id INT,
    title VARCHAR(100),
);

CREATE TABLE students (
    id INT,
    name VARCHAR(100),
);

Because the same student can have many courses and the same course can be taken by many students there is a many-to-many relationship so we create a relationship table

CREATE TABLE courses_has_students (
    id INT PRIMARY KEY,
    course_id REFERENCES courses (id),
    student_id REFERENCES students (id),
);

The question is where to store the information about exam grades.

1. Is it better to have table grades that reference the courses_has_students table;

CREATE TABLE grades (
    courses_has_students REFERENCES courses_has_students (id),
    grade INT,
);

2. Is it better to have table grades that reference both course and students' table;

CREATE TABLE grades (
    course_id REFERENCES courses (id),
    student_id REFERENCES students (id),
    grade INT,
);

3. Is it better to add a new column grade for the course_has_students

CREATE TABLE courses_has_students (
    id INT PRIMARY KEY,
    course_id REFERENCES courses (id),
    student_id REFERENCES students (id),
    grade INT
);