The most important thing is to keep yourself occupied.
Giải chi tiết:
occupied = bận rộn
A. bận
B. thoải mái
C. rảnh rỗi
D. thư giãn
Around 150 B.C. the Greek astronomer Hipparchus developed a system to classify stars according to brightness.
Population growth rates vary among regions and even among countries within the same region.