believe in在字典里的三种用法：

1.believe in sb/sth：to feel certain that sb/sth exists

2.believe in sb: to feel that you can trust sb and/or that they will be successful

3.believe in sth: to think that sth is good, right or acceptable

请问：believe in luck 和 believe in the strength of young people 该用以上哪种用法来理解？