Đọc kỹ đoạn văn sau và chọn phương án đúng (A hoặc B, C, D) cho mỗi câu từ 1 đến 12. Galaxies are not evenly distributed throughout the universe. A few are found alone, but almost all are grouped in formations termed galactic clusters. These formations should not be confused with stellar clusters, globular clusters of stars that exist within a galaxy.
