如图所示，皮带传动装置，在运行中皮带不打滑，两轮半径分别为R和r，且 $\frac{r}{R}=\frac{2}{3}$ ，M、N分别为两轮边缘上的点，则在皮带运行过程中，M、N两点的角速度之比为ω_M：ω_N=____；线速度之比V_M：V_N=____；向心加速度之比为a_M：a_N=____．

①只有加强思想道德修养，才能真正提升诗的品格

②有了好的人品，就能创作出有诗品的优秀作品

③文如其人表明诗品是人品的派生物和附属品

④诗品与人品的背离佐证了文化的相对独立性

      Are you carrying too much on your back at school? You're not alone. Back experts(专家) in the USA are worried about that young students are having back and neck problems because they are carrying too much in their backpacks .
    “It hurts my back when I run,” said Ebelin Reyes, a student in Virginia. “It's hard to get up the stairs with my backpack because it's too heavy.” Students have to carry heavy backpacks on their backs for a whole week’s study. Ebelin is one of them. They have   regular(固定的)backpacks with two straps(带子) to carry them, but a number of students with heavy loads(负担) have switched to rolling backpacks. The backpacks have wheels and can roll on the ground. Shirley Park's backpack weighs 10 kilos, and she said, “I'll change to a rolling backpack because I am starting to have back pain.”
     How much is too much? Experts say that students should carry no more than 10% to 15% of their own body weight. A few students have had a good idea to lighten(减轻) the load: less homework.
Doctor's suggestions:
Lighten the load. Take home only the books the students need that day.
(2) Wide straps are better. They can send out weight over your shoulders (肩)and be sure to wear backpacks with two straps.
(3) The heaviest things should be packed closest to the back.
(4) Bend(弯曲) both knees when you pick up the pack, don't just bend over the waist(腰).