How can I reference 2 different columns in 2 different tables simultaneously - database

Question

This is an assignment and I have been given this diagram for reference - https://imgur.com/gallery/wRkArmQ
There are other tables that I will include but the issue seems to be with the tables section and time_slot. In the diagram, they reference each other but I don't know how to. Any comments are helpful! I am using Oracle btw, here is the code -
create table department (
dept_name varchar(15) primary key,
building varchar(10),
budget int
);
create table instructor (
id varchar(10) primary key,
name varchar(15) not null,
dept_name varchar(20) not null
references department(dept_name) on delete cascade,
salary int not null
);
create table course (
course_id varchar(10) primary key,
title varchar(10),
dept_name varchar(15)
references department(dept_name) on delete cascade,
credits int
);
create table classroom (
building varchar(10) not null,
room_no varchar(5) not null,
capacity int not null,
primary key (building, room_no)
);
create table section (
course_id varchar(10) not null
references course(course_id),
sec_id varchar(10) not null,
semester varchar(10) not null,
year varchar(10) not null,
building varchar(10) not null
references classroom(building),
room_no varchar(5) not null
references classroom(room_no),
time_slot_id varchar(5) not null
references time_slot(time_slot_id),
primary key (course_id, sec_id, semester, year)
);
create table time_slot (
time_slot_id varchar(5) not null
references section(time_slot_id),
day varchar(10) not null,
start_time date not null,
end_time date not null,
primary key (time_slot_id, day, start_time)
);
create table teaches (
id varchar(10) primary key
references instructor(id) on delete cascade,
course_id varchar(15) not null
references section(course_id),
sec_id varchar(5) not null
references section(sec_id),
semester varchar(15)
references section(semester),
year int not null
references section(year)
);
create table student (
id varchar(10) not null primary key,
name varchar(20) not null,
dept_name varchar(15) not null
references department(dept_name) on delete cascade,
tot_cred int not null
);
create table advisor (
s_id varchar(10) primary key
references student(id) on delete cascade,
i_id varchar(6)
references instructor(id) on delete cascade
);
create table prereq (
course_id varchar(10)
references course(course_id) on delete cascade,
prereq_id varchar(10)
references course(course_id) on delete cascade,
primary key (course_id, prereq_id)
);
create table takes (
id varchar(10) not null
references student(id) on delete cascade,
course_id varchar(10) not null
references section(course_id) on delete cascade,
sec_id varchar(10) not null
references section(sec_id) on delete cascade,
semester varchar(10) not null
references section(semester) on delete cascade,
year int not null
references section(year) on delete cascade,
grade varchar(10) not null,
primary key (id, course_id, sec_id, semester, year, grade)
);
This is the output -
Table created.
Table created.
Table created.
Table created.
ORA-02270: no matching unique or primary key for this column-list
ORA-00942: table or view does not exist
ORA-00942: table or view does not exist