题目

You may want to know something about students in other countries: Do they also have so much homework? What do they do in their spare time?On April 8, a report came out on the lives of high school students in China,Japan, South Korea and the US. It surveyed around 6,200 students from the four countries last year. You will find the answers to many of your questions in this report.Who studies hardest?Chinese students spend the most time studying. Nearly half of Chinese students spend more than two hours on their homework every day. That’s much more than students of the US (26.4%), Japan (8.2%) 育种专家采用诱变育种的方法改良某些农作物的原有性状，其原因是诱变育种(　　)A. 提高了后代的出苗率 B. 提高了后代的遗传稳定性C. 产生的突变大多是有利的 D. 能提高突变率以供育种选择