某市2009年初拥有汽车40万量，每年年终将有当年汽车总量的5%报废，在第二年年初又将有一部分新车上牌，但为了保持该市空气质量，需要该市的汽车拥有量不超过60万量，故该市采取限制新上牌车辆数的措施进行控制，所以该市每年只有b万辆新上牌车．

（1）求第n年年初该市车辆总数a_n（2010年为第一年）；

（2）当b=4时，试问该项措施能否有效？若有效，说明理由；若无效，请指出哪一年初开始无效．

（参考数据：lg2=0.30，lg3=0.48，lg19=1.28，lg21=1.32）

单词拼写: 根据句意及首字母完成单词

1. Your lifestyle is different from o________________.

2. Wool comes from s______________.

3. They are twins. No wonder they look so s_________________.

4. The camel t__________ I rode had a bad temper.

5. Don't drive after you drink strong w_____________.

6. The wine was made from g_____________. It tastes well.

7. Look, the kangaroos are jumping a______________ our car.

8. The police only told us some facts, they didn't tell too much d____________.

9. People are warned not to swim in the sea, because there're some s_________________ in it.

10. Her hair is going g____________ with worry.