下面语段第一层次复句关系分析正确的一项是 ( ) 掌柜是一副凶脸孔，主顾也没有好声气，教人活泼不得;只有孔乙己到店，才可以笑几声，所以至今还记得。（《孔乙己》）

By the end of last week, she______in the west of China for two months helping the homeless children.

________ his spare time that his English has improveda lot

It’s not right ________others’ homework.

The researchers found clear and convincing evidence ________ happiness is the key when it comes to better health and longer lives