玉米制种中如果发现母本发育慢，可提早对母本带叶去雄，母本花期可提前。
参考答案：对
It’s hard-working ____ him to spend three hours ____ the library on Sunday.
A．for; in
B．for; on
C．of; in
D．of; on
简述我国课程改革的发展趋势。
