Prior to World War I, 20 percent of American homes had electricity.
Giải chi tiết:
Đáp án là C. Prior to = Before: trước khi >< After: Sau khi
During: trong, trong suốt ( quá trình ) … , Despite: mặc dù …
Biogas can be utilized for electricity production, cooking, space heating, water heating and process heating.
Population growth rates vary among regions and even among countries within the same region.
Around 150 B.C. the Greek astronomer Hipparchus developed a system to classify stars according to brightness.