一、语法选择（共15小题；每小题1分，满分15分）
阅读下面短文，按照句子结构的语法性和上下文连贯的要求，从1~15各题所给的A、B、C 、D项中选出最佳选项。
Homework can put you in bad mood, but that might be 1 good thing. New research shows that being too happy can sometime 2 your learning performance.
Researchers wanted to know 3 mood would affect the way children learn. So they decided 4 a study.
In the study, each child 5 20 problems. In each problem a small shape was hidden inside a 6 , larger shape. The children had to find the small shape while they were listening to either happy 7 sad music.
To measure their mood, the researchers asked the children 8 to one of the five faces, from laughing 9 crying. Children who listened to happy music pointed to the 10 faces, showing that they felt 11 .
