A．It can give a student a sense of achievement. 
B．It can help a student to prepare for future work.   
C．It can give a student nothing but trivial training.
D．It is a good way to practice the skills learnt in school.

A．He will be regretful in the future.   
B．He should restart his study in school.           
C．He may also do well in his future work.
D．He should pay more attention to his study.

A．A hypothesis that explains how changes in Earth's motions affect climate.
B．A hypothesis that explains why the shape of Earth's orbit varies over time.
C．Reasons it is difficult to find evidence to support hypotheses about the climate.
D．Analyses of the accuracy of data collected in different ways.