Danh sách tổng hợp ở đây rất đáng để khảo sát: https://wakelet.com/wake/8e074820-d496-4024-8cee-ad1a4321589a
Free, Online Learning Resources When Coronavirus Closes Schools | Cato @ Liberty
Fortunately, there are numerous online learning resources that families can take advantage of, including many that are free. Some of these resources have paid or premium options if you choose, but even the free versions offer great features and functionality.