选词填空。

1. A teacher works in a _______________ (shop, school, mall).

2. A waiter works in a _______________ (shop, restaurant, market).

3. A _______________ (businessman, doctor, cashier) works in an office building.

4. A clerk works in a _______________ (department store, school, gym).

5. A _______________ (cashier, businesswoman, waitress) works in a department store.

简述研究疾病年龄分布的方法。