一次物理课上，老师拿出了4个表面涂着相同颜色漆的大小不同的实心正方体金属块（上面分别标着1、2、3、4四个数字，漆的质量、体积都忽略不计），老师告诉大家画中两个是铁块，另两个是铜块（ρ_铜＞ρ_铁），同学们测量了每个金属块的质量和体积后，老师在黑板上用描点法画图象，如图所示，刚刚描好对应的四个点，聪明的小阳就知道了哪两个是铜块哪两个是铁块．请你判断金属块2是____ 块，和金属块3是同样材料做的是金属块____ 

如图所示，入射光经平面镜反射后，反射光线与镜面的夹角是30°．请根据光的反射定律画出入射光线，并标出入射角的度数 。

    How do you spend your time at school? Do you know how students in other countries study every day? Here are the studying ways in some western schools.

American Students

    American students spend seven hours in their schools every day. And the day is divided（划分） into classes of about 40 to 50 minutes. Students study English, history, math, science, art and foreign languages. They go to listen to different lessons taught by different teachers in different classrooms. After class they learn job skills. Sometimes they study by working in an office, a hospital or other places one day a week.

German Students

    German students love practicing. Lots of schools have lessons for only half a day. They spend most time practicing. Teachers give students enough freedom. Students may try all kinds of ideas they have. They begin to plan what they will do in the future and work hard at a young age.

French Students

    French students like independence（独立） and freedom. Their school life is very relaxing and interesting. When they have tests, they may have snacks. For example, they can put a few desks together, and put some peanuts （花生）or candies on them.